Defending champions Munster will be keen to get their campaign back on track against Clermont Auvergne at Thomond Park after going down to the French Top 14 side last weekend.

A capacity crowd will pack themselves into Munster's recently re-vamped home in the hope their side can reverse the 25-19 loss suffered at Stade Marcel Michelin. The Munster side shows just one change from the side that started in the game in Clermont last Sunday with the fit again Jerry Flannery taking the place of Frank Sheahan. Barry Murphy sat out a session this week because of a slight back problem but is expected to be fit to take his place alongside Lifeimi Mafi in the Munster midfield.

"Every game in the group is vitally important and we are only halfway through," said Munster captain Paul O'Connell. "And this Pool is wide open. Sale did well to get a bonus point on Friday night so it's going to be very tough for us. We're still right in the mix so it's in our hands - we just need to get it right this weekend."

Elsewhere, Montauban play host to pool leaders Sale Sharks on Saturday with the Premiership side hoping to conjure a repeat victory over their French rivals following their 36-6 bonus-point win last Friday.

Andrew Sheridan returns to the starting line up for his first start since October while Mathew Tait also starts at fullback, in place of the injured Rory Lamont and Luke Abraham also returns after injury.

Director of Rugby Philippe Saint Andre said, "Group A is wide open but if we want to get out of it and qualify for the quarter finals we have to aim to win all our remaining games, starting tomorrow. It's no good trying to rely on going through as a 'best second placed club', Group A is by far the toughest group, no team has a 100% record and we need to do our best to qualify."

Montauban have bolstered their line-up for the return clash with speedster Vilimoni Delasau back on the wing and captain Marc Raynaud named in the backrow.

The Pool 2 action gets underway on Friday night with Castres playing host to Leinster at Stade Pierre-Antoine. The Irish province have three wins out of three and if they can inflict more woe on the win-less French side, following their 33-3 victory last weekend, they will be on course for a home quarter-final.

Simon Keogh starts on the right wing for Leinster after scoring a try last weekend while a fitness test will be made on skipper Brian O'Driscoll after he was forced out of last week's match with ahamstring strain. Should he fail to recover, Felipe Contepomi will start with Fergus McFadden coming on to the bench.

In the pack, Malcolm O'Kelly continues his second row partnership with Devin Toner who was the Heineken Man of the Match in the 33-3 victory. Shane Jennings returns from injury and Isa Nacewa is named on the bench.

In the pool's other game Wasps take on Edinburgh at Adams Park on Sunday hoping to build on their 25-16 victory at Murrayfield last weekend. Victory will keep the pressure on Leinster ahead of the final two pool clashes.

Wasps boss Ian McGeechan has recalled Dave Walder to fly-half, switching with Danny Cipriani who takes a seat on the bench after suffering from a sickness bug this week. Second row Simon Shaw also returns with George Skivington named amongst the replacements. The bench also features Tom Voyce and Joe Worsley who return from injury.

Phil Vickery will again captain the side, with Raphael Ibanez ruled out of play for the next six weeks following a series of concussions. Head Coach Shaun Edwards said, "Last week we saw a very tight game that could have gone either way. We are delighted with the win but we know we are in a sudden death situation and any losses in the next few games will prevent qualification.

"We are expecting a huge game from Edinburgh, they are a strong side and they have a huge international presence, with many of the players having just featured in the Autumn series. For us it is good to be back at home for such an important game, with our fantastic support we will be looking to the stands to boost the team and hopefully secure the win that will keep our Heineken Cup campaign alive."

Andy Robinson has made three changes to Edinburgh's starting line-up with Hugo Southwell, Scott Newlands and Andrew Kelly all drafted in. Fullback Chris Paterson is absent after suffering a rib injury during the previous meeting while flanker Ross Rennie has to serve a two-week ban after being cited.

"Teams like Wasps and Leinster know how to win these games at the highest level," said Robinson. "We need to understand how to win games at this level, how to nail down these games, to show we have the flexibility to change tactics and the understanding of when to change tactics. There is a balance between playing with the ball in hand and the need not to get hit behind the gain line. At the weekend, every time we got hit behind the gain line Wasps scored. Sometimes you get away with it in the Magners League, last week we did not get away with it."

Leicester will be hoping to cement their place at the top of Pool 3 when they travel to Perpignan on Sunday. Fresh from a 38-27 victory at Welford Road the former European champions will be hoping to spoil Dan Carter's debut for the French Top 14 side.

Carter steps in at No.10 after watching last weekend's games from the sidelines with David Mele making way. Elsewhere flanker Gerrie Britz and lock Olivier Olibeau come in for Jean-Pierre Perez and Rimas Alvarez Kairelis respectively. The replaced players drop to the bench where they are joined by centre Jean-Philippe Grandclaude who has recovered from a leg injury.

"The boys created a few opportunities but didn't finish them off," said Carter. "The Leicester pack really dominated. There are a few things we've been working on to counter that and hopefully we can turn the scoreboard around this weekend."

Tigers head coach Heyneke Meyer has named an unchanged starting XV with the only change to the matchday 22 the inclusion of England international scrum-half Harry Ellis on the bench after his recovery from a back injury which forced his late withdrawal last Saturday.

"This is a new experience for me as a coach, sending a side out against the same opposition in successive weeks," said Meyer whose team have beaten the Ospreys and Perpignan at home and Benetton Treviso away in the Heineken Cup this season. "The players can take confidence from the win last weekend but that game is over now, they have to go out and perform again. We have to be completely focused on this game and we are definitely looking forward to it."

Elsewhere in the pool, the Ospreys will be looking for another maximum against Benetton Treviso following their thumping 68-8 victory in Swansea last weekend. Another bonus-point win would keep the pressure on the Tigers. Centre Gavin Henson has recovered from an Achilles' tendon injury that sidelined him for Wales' autumn internationals - but will not be involved in Italy. Henson will remain at home with his partner, singer Charlotte Church, who is due to give birth to their second child.

Captain Ryan Jones is still sidelind with a foot injury and prop Paul James will lead the side at the Monigo Stadium. Nikki Walker is also ruled out after picking up a serious hamstring tear last time out while winger Tommy Bowe will have the opportunity to beat his four-try haul last weekend.

"I was pleased by the ruthlessness we showed in the first Treviso game, we didn't let up in the second half, after we had secured a bonus point, we kept on going until the final whistle and scored some late tries to round off the win," explained coach Sean Holley. "We are under no illusions that it will be difficult, but we've worked hard this week on making sure that we stay focused, we've worked on a few areas for improvement from the last game and we are confident of producing a performance to the required standard.

"What made me particularly happy though was that having conceded an early try we were able to close them out of the game and didn't concede a second, meaning we have only conceded one try in three ERC games so far. A lot of the attention we receive is based on the flair players that we have available to us, but we take great pride in our defence, which has proven to be the basis of our successes to date."

Harlequins entertain Stade Francais at the Twickenham Stoop on Saturday determined to follow up their 15-10 victory in Paris last weekend with another strong showing. That victory put them in pole position in Pool 4 but they will have to be on their guard to prevent the French Top 14 high-fliers exacting immediate revenge.

The Quins starting line-up remains the same, with the only two changes being seen on the bench with Andy Gomarsall replacing Junior Poluleuligaga and De Wet Barry replacing Tosh Masson.

"Stade Francais have nothing to lose. They are a world-class side, with some great players. They will be very physical and mentally prepared for us," said Quins hooker Tani Fuga. "Saying all that, we will be equally prepared and have the advantage that we have already defeated them."

Stade Francais coach Ewen McKenzie has opted to make some changes as his side look to get their euro campaign back on track. Juan Martin Hernandez moves to fullback with Brian Liebenberg stepping in at fly-half. Mathieu Bastareaud switches to inside centre and will be partnered by Stephane Glas. Mark Gasnier and Mirco Bergamasco will fill the wing positions.

In the forwards, Sergio Parisse and Juan Leguizamon switch positions, Mauro Bergamasco joins them in the backrow and Pierre Vigouroux is preferred to Simon Taylor in the second row.

The other match in the pool sees the Scarlets play host to Ulster on Friday night a week after their 26-17 reverse at Ravenhill. That victory kept the Irish side's quarter-final hopes alive but they will need another victory to remain in touch with the pool pacesetters.

Ulster Coach Matt Williams has named a strong side to take on the Scarlets at Parc y Scarlets with just two changes from last weekend. Paddy Wallace returns to inside centre with player/coach Paul Steinmetz named on the bench. Cillian Willis is ruled out after fracturing his cheek bone in training earlier this week, Irish International Isaac Boss starts at scrum half and Belfast Harlequins club man Paul Marshall is named on the bench.

Clinton Schifcofske returns to the squad following on from an Achilles injury which has kept him out of action for the last two months, Mark McCrea drops out of the squad to make way for the Australian player.

Williams believes his team's elusive away win is within reach, "That we have never done it is not an excuse. It is completely irrelevant. For professionals who have beaten Munster at home, Edinburgh at home and beat a very good Llanelli side at home and then to say 'ah, but away we can't win' is not acceptable," continued the coach.

"It is not acceptable to me, it is not acceptable to anyone within the organisation. I told the boys that it is purely mental. They have got to front it up. We are staying in the hotel that we like, which we go to all the time, we know our opposition, we have played them twice, won once and lost closely, and there is no reason for us to go there with any sort of baggage."

The Scarlets are under pressure to end a miserable run of European form that has seen them fail to record a win in their last 10 outings. Prop Iestyn Thomas is out with a neck problem and his place will be taken by Phil John with Aled Hopkins drafted in as cover from the ranks of Llanelli's Principality Premiership side.

Elsewhere, Darren Daniel replaces Ceiron Thomas on the right wing to make his 50th appearance for the Scarlets. Thomas drops down to the bench while Rhys Priestland replaces the injured Morgan Stoddart at fullback. After a lengthy spell on the sidelines, Scotland second row Scott MacLeod makes a welcome return to regional action after a suspension and is named among the replacements.

Bath got the better of Glasgow 35-31 in a thrilling encounter last weekend and both sides will be looking for an improved defensive performance at Firhill on Sunday.

Returning from injury for the west country club are Joe Maddock, Danny Grewcock and co-captain Alex Crockett. And assistant coach Brad Davis believe his side can shore up their defence this weekend. "We know there were parts of the game where we let ourselves down. We know we are better than how we performed out on the pitch and the great thing is that we are playing the same team seven days later and have the opportunity to put things right."

Hooker Fergus Thomson will make his return to first team action for Glasgow in an entirely new front row from the one that faced Bath just last weekend with Justin Va'a replacing Kevin Tkachuk and Moray Low being promoted ahead of Ed Kalman. In the second row, Scotland 'A' international Dan Turner comes in for captain Alastair Kellock who is resting a shoulder injury. Dan Parks will wear the captain's armband in Kellock's absence.

Head coach Sean Lineen said: "It's important the boys make a statement after last weekend's game. It was entertaining but it wasn't a win. Bath have made it quite clear that they're coming here looking to win but the crowd at Firhill have been fantastic and they'll be our 16th man on Sunday."

Toulouse will defend their unbeaten record against the Dragons at Rodney Parade on Saturday looking for a repeat win after their 26-7 victory over the Welsh region last time out.

David Skrela returns at fly-half with Frederic Michalak dropping to the bench while Florian Fritz gets the nod at outside centre. Lock Fabien Pelous has recovered from a back injury to reclaim his spot in the second row with props Benoit Lecouls and Jean-Baptiste Poux preferred for the Rodney Parade clash.

Last weekend's game was overshadowed by a career-threatening injury to Dragons' centre Marc Stcherbina who remains in hospital in France following a successful neck operation and faces a lengthy spell on the sidelines. "We've had positive messages from Marc, and the best way to respond is to go out and put in a big performance," said Dragons skipper Tom Willis. "We want to do him justice. He has given us some fantastic messages, and he's keen for us to go out there and do a job."

Lock Adam Jones returns for the Dragons after successful surgery but No.8 Grant Webb and second row Andrew Hall miss out with a shoulder and bicep injury respectively.

Cardiff Blues are the only unbeaten side in Pool 6 and will bid to extend that record against Biarritz at the Parc des Sports Aguilera. A 21-17 victory in Cardiff last weekend cemented the Blues' place at the top of the pool but the French Top 14 side will be hoping to keep their euro dreams alive.

Blues boss David Young, who has opted for an unchanged team, said, "We'll no doubt get a warm reception in the south of France. It will be a difficult game because they are a quality team with quality players.

"They haven't played like they can in recent weeks and I'm sure they'll click soon, I just hope it doesn't happen on the weekend. Our kicking game has got to be accurate as they looked very dangerous from our mistakes last week."

Elsewhere Gloucester play host to Calvisano at Kingsholm where they will be favourites to record another maximum and keep the pressure on the Blues.

Greg Somerville, the most capped prop in All Black history, will begin his Gloucester career from the bench against the Italian side. "It's great to have someone of his calibre, reputation and experience in and around the squad and we are looking forward to introducing him to Gloucester," said head coach Dean Ryan.

"We appreciate and understand the need to do this in the right way because Greg has just come off a very demanding domestic season at home. It's important we don't rush but he is a formidable option to have and will be a huge benefit to our group of props."

Elsewhere, hooker Andy Titterrell and lock Adam Eustace return to the starting line-up while Apo Satala replaces Alasdair Strokosch at openside. In the backs, Gareth Cooper is back after international duty and will partner Ryan Lamb at half-back. Skipper Mike Tindall returns to the starting line-up following his first try of the season as a replacement last weekend and he will partner Matthew Watkins as Olly Barkley moves to the bench.

"We got the job done last weekend but not a lot more," Ryan continued. "We understood the need to chase a game in order to get maximum points and that is what we did but tomorrow our performance levels must be better. Calvisano will do everything we know they can - they will be direct and physical and we will have to manage that - but we need to put a marker down in this competition.

Heineken Cup 2008-09 - Round 4 (All kick-offs LOCAL times)

Friday December 12, 2008
Pool 2 Castres Olympique v Leinster 21.00 Dave Pearson (E) Canal+ Sport/ Sky Sports / Sky Italia /RTE*
Pool 4 Scarlets v Ulster Rugby 20.00 Romain Poite (F) S4C* / Sky Sports** / Sport+***

Saturday December 13, 2008
Pool 1 Munster v ASM Clermont Auvergne 15.30 Chris White (E) Sky Sports / France 2 / RTE*
Pool 1 Montauban v Sale Sharks 19.00 Peter Allan (S)
Pool 3 Benetton Treviso v Ospreys 14.35 Rob Debney (E) Sky Italia / Sky Sports**
Pool 4 Harlequins v Stade Français Paris 17.30 Nigel Owens (W) Sky Sports / Canal+Sport
Pool 5 Newport Gwent Dragons v Toulouse 14.30 Alain Rolland (I)
Pool 6 Biarritz Olympique v Cardiff Blues 14.35 Peter Fitzgibbon (I) Canal+ Sport / Sky Sports
Pool 6 Gloucester Rugby v Rugby Calvisano 15.00 Tim Hayes (W)

Sunday December 14, 2008
Pool 2 London Wasps v Edinburgh 13.00 George Clancy (I) Sky Sports / Sky Italia
Pool 3 Perpignan v Leicester Tigers 16.00 Alan Lewis (I) France 2 / Sky Sports / Sky Italia
Pool 5 Glasgow Warriors v Bath Rugby 14.00 Christophe Berdos (F)

* Delayed highlights ** Red button *** Delayed