Cristiano Ronaldo refuses to rule out Real Madrid exit, fuelling Manchester United transfer rumours

Ronaldo admits he may leave Real one day

(Getty Images)

Ballon d'Or holder Cristiano Ronaldo has not ruled out leaving Real Madrid one day, prompting rumours that he could eventually return to Manchester United.

The Portuguese has been regularly linked with a move away from the club in the last couple of years, with his former team often touted as a potential destination, along with Major League Soccer.

Patrice Evra revealed on Sunday that former manager Sir Alex Ferguson had told him that he was "99 per cent" sure that Ronaldo was going to return to the club in 2013, but his sudden retirement meant that a potential deal fell through.

Ronaldo has a contract until 2018 but admitted that "you can never know" what the future holds, offering no guarantee that he would finish his career at the Santiago Bernabeu.

When asked by German magazine Kicker if he could imagine leaving Los Blancos, Ronaldo replied: "Why not? I'm a Real Madrid player at the moment, but you can never know.

"You've got to do what makes you happy. Nobody knows what will happen tomorrow.

"All I can say is that I will always give my best for my club and for Portugal.'

That best may be enough to earn him a third successive Ballon d'Or in January, although Lionel Messi is currently regarded by many as the favourite to clinch that crown, having impressed in Barcelona's treble-winning season.

However, Ronaldo has no doubts who he thinks is the leading player in the world.

'Perhaps for you the best (is) Messi, another may think it's (Andres) Iniesta. I respect that, but for me I'm the best,' Madrid's record goalscorer said.

Additional reporting from PA