Ronaldo will face United at Old Trafford on Tuesday for the first time since his world record 80 million pounds (92 million euros, 120 million dollars) move to the Bernabeu three-and-a-half years ago.

"I think we obtained a good result in the opening leg in getting a 1-1 draw - the away goal gives us a certain advantage for the home leg," Rooney said, while warning that United would have to keep Ronaldo quiet if they were to reach the last eight.

"Without doubt, Cristiano," said Rooney in an exchange Sunday with Real sponsors bwin when asked who he thought posed the greatest threat.

"He is incredible. I have played with him and I know just how good he is.

"He is the player I have the most respect for in their team as a footballer and as a person."

Real midfield star Kaka meanwhile said that the Spaniards were not feeling they had missed their chance by failing to obain an opening leg lead.

"The feeling was we could have won it but it wasn't to be. Now the team goes to Old Trafford full of confidence to get a win there," Kaka told bwin, adding that the United players he most rated and respected were Rooney and Robin Van Persie.