Toni Nadal doesn't know when Nadal will stop playing but he is certain that he'll continue playing as long as he can win titles.
Nadal as any great tennis player is motivated by winning and as long as he is capable of winning trophies, he'll continue playing. That is according to his longtime mentor and uncle Toni Nadal who was the one that introduced him to the sport initially.
Speaking to Diario AS, Toni Nadal:
“I think that as long as he feels he has a chance of winning, he will continue. When he sees that he has no options, if he goes to a tournament and has no chance of winning, I don’t think he will play. In the end, he has won too much to fold badly.’“How much time does Rafa have left? I don’t know, it will clearly depend on his rivals, on his body…”
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"It could have been an extraordinary season, but it has been marred by the continual inconvenience he has had. The results went well because he won Australia and Roland Garros, but you leave with a bitter taste in your mouth. At Wimbledon he couldn’t play a semifinal when he was playing well and was a clear candidate for the title, there were also problems in New York… What an athlete wants above all else is to be well and play, and also win.”