The trouble that erupted inside and outside the Stadio Olimpico last week has led to fears of reprisals and possible attacks on the Italians' 3,800-strong support at Old Trafford.

Sir Alex Ferguson has already attempted to play down such fears, insisting the Roma fans will be safe during their stay in England.

And Totti has urged any visiting supporters thinking of causing trouble not to.

"I want our fans to be happy and for them to enjoy the experience of being here," said Totti.

"Being a football fan is about supporting your team and I would appeal to ours to just enjoy the performance we intend to put on for them tomorrow."

There have been reports some of Roma's notorious `Ultras' will be at the game, increasing possibility of the violent scenes that scarred the first meeting.

However, Roma coach Luciano Spalletti backed up Totti's words.

"Our fans have to behave in keeping with what is a wonderful sporting occasion," he said.

"They are part of the growth spurt we are enjoying as a club and if they appreciate what we are doing, good behaviour will come spontaneously."

Enjoying their best run in the competition since they were beaten by Liverpool in the 1984 final, Roma could be regarded as favourites given United have failed to overturn first-leg deficits five times in Champions League combat.

However, Spalletti, who is likely to replace suspended midfielder Simone Perrotta with David Pizarro, claims it is United who have all the European credentials.

And while the hosts may be affected by injury and the banned Paul Scholes, Totti acknowledges that in Cristiano Ronaldo, the Red Devils have a player capable of winning any game.

"Ronaldo can decide a match on his own," observed Totti.

"You see what he can do, not just against us last week, but regularly in the Premiership, and it seems he is capable of doing just about anything.

"He can make the difference in this game tomorrow but we just have to hope he doesn't play well."

With Perrotta missing, Totti will be one of two World Cup winners in the Roma starting line-up.

However, as a lifelong fan of the club, the 30-year-old has no doubt what was the bigger occasion.

"It is an important game. As a Roma fan, it is more important than the World Cup final," he said.

"We are playing against a huge team, with great qualities.

"But we have beaten them once already and we have to show the same attitude as we did against Lyon in the last round.

"I had a good feeling before that game and I have a good feeling now.

"We deserve to be where we are and hopefully we can reach another historic milestone for this club."