Manchester United [Images] manager Alex Ferguson rates Tuesday's Champions League tie with AC Milan in Italy [Images] as the toughest challenge his team has faced.

United trail 1-0 from the first leg at Old Trafford after a late Hernan Crespo [Images] strike gave the Italian champions the edge in the fight for a place in the quarter-finals.

"It is probably the hardest task we have had to face given as we are 1-0 down but I hope we can score the goal that changes the game," said Ferguson, who will be without regular right back Gary Neville after the England [Images] international was ruled out with an ankle injury.

"At this level an away goal counts for a lot and you saw that in the faces of the players after they scored. We hope we can do the same," the Scotsman told a news conference on Monday.

United have enjoyed some success against Italian teams in the Champions League in recent years. Ferguson said that the victory over Juventus in 1999, when his team came back from 3-1 down on aggregate to beat the team then coached by current Milan boss Carlo Ancelotti, showed what his players were capable of.

"It serves to remind everyone, including Milan, that is possible for us to do this," said Ferguson. "It is not the easiest task but it is not impossible."

Ferguson said that despite the face United have to score to have any chance of progressing in the competition it would be vital to keep things tight at the back.

"That's the key to the game. If we can keep Milan out that gives us a great chance. Even at 20 minutes out (from the end) and the score at 0-0 I would be happy," he said.

NISTELROOY PRIMED

Ferguson repeated his view that his current side is the better than the one that went on to win the Champions League in 1999, highlighting the presence in his side of youngsters Wayne Rooney [Images] and Cristiano Ronaldo [Images] as well as Dutch striker Ruud van Nistelrooy [Images].

Van Nistelrooy made his return from an injury lay-off in the first leg, played in Saturday's goalless draw with Crystal Palace and could feature from the start at the San Siro.

"I feel I'm improving. I had 20 minutes against Milan two weeks ago but I've had two full games since then and all the training as well and I feel I am improving.

"I feel good. Physically I am at my best and I hopefully I can show that as well tomorrow on the football side," said the forward.

Van Nistelrooy was unable to find the target at Palace but Ferguson is hopeful that it will be a different story against the Italians.

"Hopefully he will get the same sort of chances he had on Saturday....I hope he gets the chances because there is no-one better in the box," the United boss said.

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