Roma 0
Man United 2

Cristiano Ronaldo has been accused of showing a lack of respect to Roma by the Italians' midfielder David Pizarro.

The Portuguese winger scored his 36th goal of the season in Manchester United's 2-0 victory in their Champions League quarter-final tie in the Italian capital last night.

The one blight on the evening for United was the knee injury sustained by defender Nemanja Vidic, who will have a scan on the problem today and could miss the run-in to the end of the season.

Pizarro, who was booked for a foul on Ronaldo in the first half after the 23-year-old had teased the Chilean's team-mate Marco Cassetti with a series of step-overs, was unhappy with Ronaldo's attitude and hinted that their feud could spill over into the second leg.

Pizarro said: "Beyond the fact that Ronaldo is a fantastic player, he is also very cocky and does certain disrespectful things on the pitch.

"We will have something to say to each other in the return leg."

As Roma struggled to deal with Ronaldo and Wayne Rooney, who scored the second goal after 66 minutes, Pizarro's words represented little more than sour grapes although United boss Sir Alex Ferguson will attempt to ensure his star man is given adequate protection in the return leg next week.

Ronaldo's brilliant header six minutes before half-time gave United the advantage and their lead was doubled when Rooney pounced on a mistake by Roma keeper Alexandre Doni to scramble the ball in from close range.

Ronaldo insisted his fancy footwork had not been intended to wind up Luciano Spalletti's side. He said: "I have always done those tricks, even three or four years ago, because they are part of my game.

"But they are tricks I do for the good of the team, rather than to irritate the opposition. That is not how I play."

Of far greater concern for Ferguson will be the condition of Vidic, who limped off after 33 minutes of the tie after he had landed awkwardly, jarring his knee, following an aerial challenge with Roma forward Mirko Vucinic.

Vidic's defensive partnership with Rio Ferdinand has been the foundation on which United's success over the last two seasons has been built. If the Serb is ruled out for a significant period, it would hand a huge boost to Chelsea and Arsenal in the race for the Premier League title.

Ferguson said: "I pray it is not serious because he is an integral part of our team. It might just be a nerve injury but we can't be sure."

With Barcelona having won 1-0 away at German club Schalke in the first leg of their quarter-final last night, a last-four tie between two of the giants of European football appears a virtual certainty.

But after watching his team ride their luck early in the second half when Roma were only a goal down, Ferguson knows it would be foolish to underestimate Spalletti's men.

He said: "It was a fantastic result for us but I will probably start to worry about it on the day of the game.

"The first thing we have to do is prepare properly for the match. We cannot take anything for granted with a place in the semi-finals at stake."

There was no repeat of the violent scenes that have marred clashes between the clubs in recent matches, and the United manager said: "That is a bonus and what we wanted to happen.

"Roma and ourselves worked hard to make sure there would be no incidents."