Spanish tennis star Rafael Nadal said on Thursday that he is a "completely clean guy" and denied having used performance-enhancing drugs.The 29-year-old was asked about his reaction to Russian tennis star Maria Sharapova's failed drug test and he took the opportunity to explain speculation about him."I am a completely clean guy. I have never had the temptation of doing something wrong," Nadal was quoted as saying by the BBC on Thursday."I believe in the sport and the values of the sport.It is an example for the kids and if I am doing something that goes against that, I will be lying to myself, not lying to my opponents."Nadal has never failed a drug test but has been the subject of speculation that he dopes.Nadal also said that Sharapova who tested positive for Meldonium a few days back deserves punishment."It is difficult to imagine that something like this can happen, but mistakes happen," he said."She should be punished.""I want to believe it is a mistake for Maria. She didn't want to do it. But obviously it is negligence. She must pay for it."