Sir Alex Ferguson feels winning more Champions League titles will be key to keeping Cristiano Ronaldo in the long term.

Ronaldo's future is once again a hot topic for debate with Real Madrid tipped to launch a world record bid for the Manchester United winger this summer.

United boss Ferguson criticised Real's underhand tactics on Friday, but stressed his confidence that Ronaldo will still be at Old Trafford next season.

However, Ferguson has acknowledged that, two or three years down the line, United may face a greater challenge to hang on to the 23-year-old.

Following the midweek Champions League win over Chelsea, Ferguson hopes further European successes will persuade Ronaldo to stay with the club.

"He's 23 years of age and I think that when he gets to 25, 26, he will have a big decision to make then," said Ferguson in The Sun.

"That will be the biggest task when he gets to that age.

"How big we are then, in terms of European championships, that will resonate with him and be very, very important to this club.

"That's why I make the point of winning European trophies - we've got to do better at that. And we have got the structure here."

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