Manchester United manager Alex Ferguson has insisted that his side can reverse the misfortune of their 2-1 defeat to Porto on Wednesday, saying that the Old Trafford atmosphere will lift a squad depleted by the suspension of their regular source of inspiration, Roy Keane.

Keane's 87th-minute dismissal on Wednesday, for stamping on Porto goalkeeper Vitor Baia, resulted in an automatic ban from the second leg, but Ferguson yesterday said that meeting will be formidable for Porto thanks to the passion at the Theatre of Dreams on big occasions.

"Old Trafford is a very difficult place to win at on major European nights," said Ferguson. "Our record there is outstanding and hopefully we will produce a performance when it matters. We still have a good chance of going through and Porto recognise that."

The sentiment was echoed by winger Ryan Giggs who promised the club's fans that the team will bounce back from the defeat.

But, while he attempted to be positive, Giggs is also acutely aware that the comprehensive manner in which his team were out-played at the Estadio do Dragao does not hold out too much hope of completing United's first comeback in a two-legged European tie since the famous defeat of Barcelona 20 years ago.

"We didn't play anywhere near as well as we can," said Giggs. "It's disappointing because we have the ability to do a lot better.

"We will need to do that in the second leg and I am confident we will. We will always create chances at Old Trafford and we only need one goal to put us through."

But United not only have to score but also prevent more leakage of goals via a shaky defence that after Wednesday's game has conceded 13 goals in its last six games. And there appear few signs of a combination capable of shoring up the holes.

A fledgling central defensive partnership between Gary Neville and Wes Brown encouragingly stood firm for long periods against a tidal wave of Porto attacks, but unfortunately Ferguson will have to immediately rip it apart.

Neville is suspended for the next four domestic games and by the time he returns for the trip to Arsenal, on March 28th, Mikael Silvestre is expected to have recovered from his ankle ligament injury.

It means the United boss must decide whether to recall out-of-form John O'Shea, who was restricted to a brief substitute appearance last night, to play with Brown at Loftus Road on Saturday, or haul Keane back from his favoured midfield berth where there are more options available to fill the hole.

It is an ominous situation but Giggs is refusing to get downcast. The most decorated player in United history firmly believes they will turn their European campaign around.

"The away goal could turn out to be so important," he said. "Porto looked nervous early on, even if we didn't capitalise fully on that and even in the second half, though they had most of the possession, they didn't create much.

"Those are positive things to take out of the game and that at least gives us something to build on."