Asked yesterday whether he could name a team in Europe playing football as stunning as that produced by Manchester United in their past two matches, Sir Alex Ferguson opted to answer a different question. The United manager knows from his decades of experience that form is transient, that fate is fickle and, above all, that this much-admired United team have still to prove, at least on the Champions League stage, that they have the substance to accompany their undoubted style.

AS Roma know more than most about United's strengths, having been on the wrong end of a 7-1 hammering in the quarter-final, second leg last season at Old Trafford, but the Italian club can also draw from the experience of having beaten Ferguson's team 2-1 in the first leg of that tie.

It is easy to forget how comprehensively outclassed United were in the first half of that game in the Olympic Stadium, one of many uncomfortable European expeditions for a team who, remarkably, have won only four of their past 18 away games in the Champions League, a sequence dating back to the 2003-04 campaign.

United's form in Europe has picked up considerably over the past 18 months, yielding victories away to Benfica, Lille, Sporting Lisbon and Dynamo Kiev, but not enough to dispel the belief within the Roma camp that Ferguson's team are vulnerable away from Old Trafford.

“They are the best team in the world, very, very good, but it's a long time since they got a very important win abroad,” Daniele De Rossi, the Roma midfield player, said. “They're fantastic in Manchester, but they're not so good away. They never dominate a match away in Europe.”

A team could conceivably win the Champions League without ever dominating an away match, but Ferguson will hope that his team can prove this evening, in one of the most hostile arenas in Europe, that they are far from a soft touch. Yesterday, as he lauded the virtues of youngsters such as Anderson, Cristiano Ronaldo and Wayne Rooney, Ferguson said that he was “not even slightly worried about their temperament”, adding that “they all have the quality to play on the big occasion”.

It takes more than quality, however, and more than temperament to win the Champions League. “It's difficult,” Ferguson said. “We have only won it once in my time here, so that tells you how difficult it is. But we have the players who can make us successful. They are confident they can express themselves, they enjoy playing and they are not afraid of challenges. There's enough youth in the team to make them ambitious.”

Any team hoping to conquer Europe must also enjoy a degree of luck and United will hope that the absence of the injured Francesco Totti from the Roma team is a portent of that. Ferguson suggested that he was a little sceptical of the medical bulletins from the Roma camp, calling to mind his memorable claim that “when an Italian says it's pasta on my plate, I check under the sauce”.

Perhaps Ferguson was, as he saw it, playing the Italians at their own game when he arrived in Rome citing doubts over the fitness of Edwin van der Sar, Rio Ferdinand, Patrice Evra and Michael Carrick. All four are expected to start tonight as United look to show that their travel sickness is a thing of the past.