MADRID: 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 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 percent guaranteed. As I said before, there are no certainties in football."