Manchester United face a formidable task against AS Roma at Old Trafford on Tuesday as they bid to reach the last four of the Champions League for the first time in five years.

Although Roma carry a narrow 2-1 first leg lead into the game, they played superbly in their last away match in the competition when they won 2-0 at Olympique Lyon -- and United manager Alex Ferguson is treating them with the utmost respect.

Ferguson had tipped Lyon as a dark horse capable of winning the competition -- and knows United will have to be at their imperious best to keep alive their dreams of repeating their 1999 treble when they won the Champions League, Premier League and FA Cup in the same season.

They memorably beat Bayern Munich in Barcelona to lift the European Cup eight years ago -- and the winners of this tie meet either Bayern or AC Milan in the last four.

Looking ahead to Tuesday, Ferguson said: "We have given ourselves the best advantage in that we have scored the away goal and if we win 1-0 we are through.

"But Roma's 2-0 win in Lyon was special. We have got to analyse that game. We know what they are capable of."

United will be without the suspended Paul Scholes, who was sent off in Rome last week and could be replaced by Darren Fletcher. They also have three defenders out injured -- Nemanja Vidic, Gary Neville and Mikael Silvestre.

However, United do have a formidable record at home in Europe, losing only once in their last 31 matches at Old Trafford -- but they will also quickly need to put Saturday's surprise 2-1 loss at Portsmouth in the Premier League out of their system.

BIG PITCH

After Lyon, Roma coach Luciano Spalletti believes his team can claim another high-profile victim.

 "The best way to prepare for the match of your life is with a win. Roma is ready," said Spalletti after Saturday's 2-0 victory over Catania - their first away Serie A success of 2007.

"We'll be playing on one of the biggest pitches in Europe. United have designed it that way so they can play lots of one-on-ones. Because they have a lot of individual skill, they beat players easily.

"These are qualities that we also have, though, and I'm convinced it is going to be a great match."

Several of Roma's leading players, including captain Francesco Totti, Daniele De Rossi, Rodrigo Taddei, Mancini, and Cristian Chivu, will come into the game fresh having been rested for all or most of Saturday's match.

Christian Wilhelmsson is expected to stand in for suspended midfielder Simone Perrotta. Perrotta's absence, however, is made up for by the return of Chilean international David Pizarro, whose vision has made him one of Roma's most influential players this season.

Security will be highly visible in and around the ground and the city with the police determined to ensure there will be no repeat of the violence that marred last week's first leg in Italy.

Probable teams:

Manchester United: 1-Edwin Van der Sar; 6-Wes Brown, 5-Rio Ferdinand, 22-John O'Shea, 4-Gabriel Heinze; 7-Cristiano Ronaldo, 16-Michael Carrick, 24-Darren Fletcher, 11-Ryan Giggs; 8-Wayne Rooney, 9-Louis Saha

AS Roma: 32-Doni; 77-Marco Cassetti, 5-Philippe Mexes, 13-Cristian Chivu, 2-Christian Panucci; 16-Daniele De Rossi, 7-David Pizarro; 4-Christian Wilhelmsson, 11-Rodrigo Taddei, 30-Mancini; 10-Francesco Totti.

Referee: Lubos Michel (Slovakia)