Real Madrid star Cristiano Ronaldo has admitted that there are "no certainties" over his future, and refused to rule out a move to the Spanish club's rivals Barcelona or his former club Manchester United.

The three-time Ballon d'Or winner has been heavily linked with a move away from the Spanish capital in recent weeks despite his current contract running until 2018.

Although the 30-year-old downplayed talk of a move to Paris Saint-Germain earlier this week, he refused to rule out any scenario, whether it be staying at Real for the remainder of his career, joining their biggest rivals in Spanish football, or returning to the Premier League.

"There are things that you kind of already have an idea [about], that to play one day for Barcelona would be almost impossible, or to play for another English club other than Manchester [would be] very complicated," he told The AP. "But that is not 100% guaranteed. As I said before, there are no certainties in football.

"Everything is open, all leagues. I may end my career here with Real Madrid. I am just being honest, I do not know what is going to happen tomorrow. If I was 75% certain, I would say so, it would not be a problem. But I have no idea.

"Right now I do not see myself playing in the American league, but that is right now. In two or three years I may think differently. As a football professional I prefer to stay in the present. The present is good and I am enjoying being at Real Madrid. When it is closer to ending my contract I am going to have to make decisions, whether it is staying at Real Madrid or going to another club or ending my career in a few years."

Ronaldo is Real's all-time leading goalscorer with 334 goals in 320 competitive matches.