How long do you think it will take Nadal's body to breakdown and he needs a wheelchair?

Nadal is already injured often. In the coming years he will tail back the amount of tournaments that he will play and he will focus on the slams. I think he has another 4 years in which he will at least be a threat at the majors. Federer's game is not as physically demanding, but he will retire before Rafa hangs it up.