Cristiano Ronaldo has hinted his future at Manchester United will be tied to manager Sir Alex Ferguson.

"It's impossible to stay somewhere for 100 years," said Ronaldo.

"Everything has to change at some point. But the boss is the most important person at the club and when he leaves it's going to be very difficult to replace him.

"When he retires, everyone must respect his decision. Thankfully, though, this is not the time to think about this, because right now he's in charge and everything is great.

"He has helped me so much. And I listen to him always because he has taught some of the best players in the world."