Andy Henderson admits Scotland are entering "sink or swim'' territory in the RBS 6 Nations as they prepare for the daunting task of facing Wales in Cardiff.

Defeat tomorrow in the Welsh capital would be a crushing blow for Frank Hadden's side and leave them perilously vulnerable to finishing with the Wooden Spoon for the third time in five seasons.

Centre Andy Henderson is hoping to put the nightmare of last week's 27-6 home defeat to France behind him by helping Scotland achieve a famous Millennium
Stadium victory.

But Scotland suffered a pre-match blow this morning when wing Simon Webster pulled out with a hamstring problem, meaning Chris Paterson switches to the number 11 role from full-back as Hugo Southwell comes into the side.

Scotland might be weakened by the absence of Webster, and Wales, following their startling victory at Twickenham last weekend and Scotland's defeat, are firm favourites for victory tomorrow.

Henderson admitted: ``Rugby is all about momentum and the first game in any tournament is so important - and that is especially the case in the Six Nations
which is such a short, sharp competition.

``But the championship goes on and the games are going to be there regardless, so it is a case of sink or swim for us.

``Obviously it's hard to take confidence from a defeat, but we know where we went wrong and we believe we can fix it.

``This one on Saturday has come along quite quickly and we've got to go in with belief and confidence if we are to have a chance.''

The France match was set up to be a day of double celebration for Henderson, who was winning his 50th cap on his 28th birthday.

However, the party was cut short by a Scottish performance which fell some way short of the required standard.

Scotland had gone into the match at Murrayfield with high hopes after a solid showing in last year's World Cup.

Head coach Hadden had talked before the match about competition for places in the team being ``tougher than ever'' and claimed the stability which the squad had enjoyed during the last two years could be a key factor in a successful season for his side.

But the home team were well beaten by a French side who were far better organised and in tune with one another - despite the fact six of the visiting squad members were making their international debuts and they had only had one week together to prepare for the match under new coach Marc Lievremont.

Henderson admitted his birthday was ruined.

``It wasn't an ideal way to commemorate the day, but it's over now and I am focused on helping getting our season back on track against Wales on Saturday,'' he said.

``It was tough straight after the game, but this has been a short week so we looked at the video, identified the positives and negatives, and moved on.

``You can't be dwelling on it until Thursday when you've got a game on Saturday.''

To add salt to the wound of the humbling defeat to France, Henderson spent the first half of this week waiting to hear if he would be cited for an off-the-ball incident.

Henderson became embroiled in a tussle with Damien Traille after Vincent Clerc had touched down for France's opening try, and the camera caught the Scotsman
using his head to push his opposite number away.

Achille Reali, the Italian match commissioner, eventually decided the penalty which referee Alain Rolland gave against Henderson at the time was punishment
enough.

``I thought it was dealt with on the pitch, the referee gave a penalty against me and I was disappointed with that, but I didn't think too much about it after that,'' said Henderson.

``There was a lot made of it by the press but he was unmarked afterwards and I'm glad it didn't become a major issue.

``It was what it was, we were tussling during the lead-up to the try and afterwards he came up to me quite aggressively, and we got involved in a tussle.

``Obviously I was disappointed with the way last Sunday went because all their tries were reasonably soft and the bounce of the ball obviously went their way.

``But they took their chances and fair play to them, you make your own luck and when they got the ball they controlled it really well.

``If we had been within a score at half-time and putting them under pressure then a win would have been a lot more of an achievable target at that stage, especially with the number of young guys and new caps they had in their team.

``But it was an 11-point lead at the break and that helped them a lot. It gave them a reasonable buffer and meant that there was no real reason for their inexperienced guys to start feeling the pressure.

``You've always got to keep playing and keep trying, but sometimes when you are behind and you are forcing things then that is when mistakes come.

``This week we have to make sure that we don't let them get their noses in front, because Wales are the sort of team that become very hard to stop when they think things are going their way, and all of a sudden we'll find ourselves in a similar sort of situation as we were in last week.

``And if we manage to get ourselves into the lead, we have to make sure that we close the game down.

``As we saw when they came from behind to get that victory over England last weekend, they only need to be given half a chance and they will capitalise.

``Basically we have to keep a tight rein on them, and cut out the elementary errors.''

Southwell is relishing his surprise chance to stake a claim to wear the number 15 jersey on a more regular basis.

He admits it has been tough to watch recent Scotland internationals from the bench.

``It's frustrating,'' he told STV, ``but the decision was made and I've got to make sure that now I can change that decision by putting in a massive performance tomorrow

``It's going to be tough, it's going to be a hard game, but I'm pretty confident with the experience I've got that I can go out and put in a massive performance.''