STEVE WIGLEY admits he faces a "massive decision" between keepers Antti Niemi and Kasey Keller for tomorrow's Old Trafford clash.

Niemi is seen by many as the Premiership's best goalkeeper but has not played for a month after undergoing min-or surgery on his knee, with Spurs star Keller deputising superbly in recent weeks.

The American has spoken of his willingness to extend his loan spell at St Mary's but Niemi has been back training since Monday and yesterday confirmed his knee feels "okay."

Wigley will not contemplate dropping Keller unless he is certain the influential Finnish stopper is fully recovered.

"It is a massive decision," said the Saints head coach.

"To even consider a change, Antti Niemi will have to 100 per cent.

"Kasey Keller has come in and done fabulously. It has been a difficult time - he came in when we'd just been beaten at Watford - and to get somebody of Kasey's quality and experience was a massive plus to us.

"He's played a significant part in the last few weeks.

"We're delighted with his contribution and the only way it does become a decision is that the person I've got coming back is arguably the best goalkeeper in the Premier League."

Niemi, last season's Saints player of the year, is full of praise for the way Keller has performed in recent weeks.

"He's been superb but I'm not surprised as he is a very good goalkeeper," he said.

"He has made some good saves and it's good to have competition. I started training on Monday and feel okay."

Niemi's last game was the 2-2 draw with Arsenal at Highbury and he's hoping Saints will again raise their game on a day when they are overwhelming underdogs.

"The pressure was off and we played well against Arse-nal," he said. I think against Man Utd, Arsenal and Chel-sea, it's hard to match them and you have to have a plan.

"You do have to think about stopping them, but we also have to try and keep the ball. You have to be confident and brave on the ball, which I think we did quite well against Arsenal."

As well as Niemi, Wigley has the option of bringing back striker James Beattie (calf) and Claus Lundekvam (virus), who are both fit after missing last week's 2-2 draw with Crystal Palace.

"We are getting healthier, which is important with the Christmas period coming up and the amount of games we have to play," added Wigley.