Donncha O'Callaghan (right) is an injury doubt for Munster © Getty Images

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Matches: Toulouse 23 - 9 Leicester Tigers | Racing Metro 22 - 17 Munster | Ospreys 38 - 17 Benetton Treviso | Ulster 41 - 17 Castres

Teams: England | France | Ireland | Italy | Scotland | Wales

The latest instalment of the Heineken Cup kicks off on Friday night with Europe's best sides set to go head-to-head over the coming months in the hope of securing the much-prized silverware.

Ahead of this weekend's opening round, ESPNscrum provides a run down on all the contenders.

Pool 1

Saracens travel to Edinburgh in their first match with the home side looking to improve on their outstanding campaign last season. They reached the semi-finals of the tournament before being knocked out by Ulster but their journey to the latter stages of the competition was one of the stories of the season. They will go into the match buoyed by Scotland centre Matt Scott's decision to put pen to paper on a new deal that will keep him at the club until the 2015 Rugby World Cup.

Their opponents Sarries ran into a resolute Clermont Auvergne outfit in last season's quarters but with four wins from six in the Premiership and an in-form Charlie Hodgson in their ranks, they will look to come away from Edinburgh with the spoils. England fly-half Owen Farrell is on hte bench with Hodgson retaining the fly-half shirt, with Alex Goode, Chris Ashton, Schalk Brits and Kelly Brown among those players who return after missing last weekend's Premiership victory over London Welsh.

Pool 1's other match sees Racing Metro host Munster. Olly Barkley will make his Metro debut after his shock switch from Bath while the Irish heavyweights are bolstered by lock Paul O'Connell's return following a five-month injury absence. However his regular second-row partner Donncha O'Callaghan is out with a hamstring injury while MarcusHoran is on the bench.

Pool 2

Toby Flood is likely to start against Toulouse © PA Photos

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Leicester journey to Toulouse for their opener on Sunday in one of the eye-catching fixtures of the first round. And despite George Ford getting the nod for the Tigers' most recent Premiership outing against Sale Sharks on Friday, Toby Flood will start in France. "You have to go to Toulouse with some experienced players and manage the game. It's not a place to go and blood young blokes who have never done it," said director of rugby Richard Cockerill. "Floodie will be our first choice going into Europe. He's very experienced."

Steve Mafi and Scott Hamilton are both included after returning from injury with prop Marcos Ayerza in the squad for the first time this season following his involvement in Argentina's Rugby Championship campaign. Toulouse will leave it late to decide on the fitness of Yoann Huget while Patricio Albacete could play after returning from Rugby Championship duty.

By the time the match in France kicks off on Sunday, the Ospreys will have already played Treviso at the Liberty Stadium. The pair have already met this season with the Italian side overcoming the Welsh region for a memorable 12-6 in round one of the RaboDirect PRO12. The Ospreys welcome flanker Justin Tipuric back to their pack while hooker Richard Hibbard and prop Adam Jones have shaken off injury concerns.

The Ospreys have lost the likes of Shane Williams, Tommy Bowe and Paul James since last season but flanker Ryan Jones insists that expectation is still high in the camp. "There's been a significant change that's been well-documented over the last 12 months, really," Jones said. "But from the players' point of view the expectations are still sky high. We're highly competitive. I certainly know I am and you always look forward to pitting yourself against the best teams in Europe."

Pool 3

Biarritz will hope Dimitri Yachvili provides them with some inspiration © Getty Images

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Harlequins entertain Biarritz on Saturday evening with the French side playing at The Stoop for the first time since their Amlin Challenge Cup final victory there last season. Quins have lost their last two matches in the Premiership so will hope to find a return to winning ways against the French giants. Quins were knocked out of the Heineken Cup last season after losing their final group match to fellow Pool 3 side Connacht and they will hope to right some wrongs this season. Their opponents Biarritz have won four of their eight matches this season and sit in eighth in the Top 14.

This will be Zebre's first season in the Heineken Cup and are winless in the PRO12 so far. Connacht have already played the Italian side this season and won 30-17 over in Parma at the Stadio XXV Aprile and they will hope for a similar return when they journey there on Saturday.

Eric Elwood makes four changes to his starting pack with Adrian Flavin making way for hooker Ethienne Reynecke and Denis Buckley and Nathan White forming the all new front row trio. Elsewhere in the pack, the fit again John Muldoon who returned from injury last week replaces Dave Gannon in the back row.

Pool 4

Castres' Laurent Travers has confirmed that he will leave the French club at the end of the season © Getty Images

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Ulster are the only unbeaten team in Europe's top divisions and they will be aiming to extend that record when they play host to Castres at Ravenhill on Friday. The club are still mourning the tragic death of Nevin Spence but they are in a rich vein of form in the PRO12 with five wins from five. They will be buoyed by the return of Ruan Pienaar who could play his first match for the province this season after starring for the Springboks in the Rugby Championship. Ulster have also included the likes of Stephen Ferris, Rory Best, Tommy Bowe and Andrew Trimble in their squad for the Castres match but there is no place for prop Declan Fitzpatrick who is out with a medial ligament injury.

Castres will go into the match on the back of an impressive 16-13 win over Clermont Auvergne on Friday. But coaches Laurent Labit and Laurent Travers both confirmed this week that they will leave the Top 14 side at the end of the season and it remains to be seen just how much an affect this will have on the team.

On Sunday, Glasgow Warriors journey to Northampton Saints complete with new signing Josh Strauss in their ranks. The former Lions back-row has started at No.8 and blindside for the Warriors and will be a big threat. Northampton were unbeaten in the Premiership until they ran into a rejuvenated London Irish outfit on Saturday and came away from the Madejski with a 39-17 defeat.

George Pisi has recovered from a shoulder injury to take his place in the Northampton starting line-up as one of four changes for the Saints. Skipper Dylan Hartley also returns while James Wilson is named at full-back and Rhys Oakley is at No.8.

Pool 5

Clermont will look to Lee Byrne for inspiration on Saturday © Getty Images

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Defending champions Leinster will kick start their campaign against a team playing their first match in Europe's premier tournament. The Exeter Chiefs are now in their third Premiership season and have cemented their status as one of the top flight's most consistent sides but they will have a baptism of fire in the Heineken Cup when they travel to the RDS on Saturday.

Cian Healy will make his 100th appearance for Leinster after recovering from a bicep injury while Leo Cullen also returns to partner Damian Browne in the second row having overcome an arm injury. Injury doubts about Brian O'Driscoll and Kevin McLaughlin have eased and both players are named in the starting line-up. However they will go into the match without three of their forwards with Sean O'Brien, Rhys Ruddock and Dominic Ryan all sidelined.

And while Exeter are packing down against Leinster on Saturday, Clermont will be hosting the Scarlets over in France. The news that skipper Aurelien Rougerie is set to pen a new two-year deal despite overtures from France will hand them a boost. They also boast Welsh international Lee Byrne in their squad and Clermont director of rugby Jean-Marc Lhermet is hopeful that he will play a big part in their Heineken Cup charge this term.

"The Scarlets have evolved a lot since Lee joined us," Lhermet said. "They have been through team some difficult situations but they have made a tremendous start in the PRO12. They are building a team with some young high-level players. We fear them, the first game in Clermont will be crucial, but it is the best way to start the Heineken Cup.

"Lee has brought us a lot of experience at full back along with his serenity and his reliability for the key games. Lee was very motivated for the Top 14 and has been well involved in the team. Clermont had to wait 100 years to get its first French champion title. We do not want to wait that long for a European title and we are improving more and more with a stable team."

Scarlets have named young tight-head Samson Lee in their team and coach Simon Easterby names an all-Welsh international backline, with Morgan Stoddart and George North on the wings, Jonathan Davies and Scott Williams in midfield, Tavis Knoyle and Rhys Priestland at half-backs, and Liam Williams at full-back.

Pool 6

Toulon's Delon Armitage will hope to make a dent in the Heineken Cup © PA Photos

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The Top 14 league leaders Toulon's big spending is showing no signs of abating with former Springbok forward Danie Rossouw the latest to be added to the long list of galacticos to have been lured by Mourad Boudjellal cheque book. He will not arrive until February but they have a galaxy of stars chomping at the bit to make a dent in what is only their second Heineken Cup. They will start their European campaign against fellow French side Montpellier in the final match of the opening weekend on Sunday. Montpellier have been without their Argentinian contingent in recent weeks with a host of their players turning out in the Rugby Championship but they will hope to have their services at their disposal sooner rather than later.

In Pool 6's other match, Bryan Redpath's hapless Sale will host the Cardiff Blues at the Salford City Stadium. While the Blues are worrying over Jamie Roberts' future, the Sharks have a more immediate concern with no wins in their opening six matches. They appear to be on the verge of tying down former Lions boss John Mitchell as their new forwards coach and they will eye the competition as a welcome respite from the Premiership. Coach Redpath is optimistic that they will fare well in the competition despite their woeful showing in the Premiership.

"We have to show that mentality in every game, starting with Cardiff on Sunday, and get that first win," Redpath told the BBC. "It's little things we need to go our way. When things are tough they're tough, but we have to stay strong together."