Cristiano Ronaldo is really serious about keeping his options open for the future. Not even Barcelona or Manchester United's rivals in England are off limits.

Ronaldo told the Associated Press on Thursday that he knows it would be "very complicated" to play for these clubs, but it's something that the Real Madrid star doesn't rule out either.

He said nothing is certain in soccer, so he will not close doors to any leagues or teams, not even Madrid's biggest rival.

“It's a little more difficult, but ...,” he said, with a long pause, not dismissing the possibility.

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

In his interview with the AP, the Portugal forward made it clear that when time came to decide about his future, he will consider all options on the table.

"Everything is open, all leagues," he said. "1 may end my career here with Real Madrid. I'm just being honest. I don't know what's going to happen tomorrow. If I was 75% certain, I would say so, it wouldn't be a problem. But I have no idea."

Speaking before the launch of his new product with nutrition partner Herbalife, Ronaldo said he may even decide to be somewhere else other than Europe, and that it's not impossible for him to be playing in the United States' Major League Soccer.

"Right now I don't see myself playing in the American league, but that's right now," he said. "In two or three years I may think differently."

He said that in the future he may be at a stage of his life in which he might prefer playing in the US, instead of the more traditional European leagues.

"These are always difficult questions to answer because we never know what's going to happen tomorrow," he said.