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I am a completely clean guy - Rafael Nadal

Rafael Nadal has denied he has ever used a banned substance to get an edge or to speed up recovery from injury.

Asked for his reaction to Maria Sharapova's failed drug test, the 14-time Grand Slam champion took the opportunity to address speculation he has used performance-enhancing drugs.

The Spaniard, 29, said he was "a little bit tired" of the rumours, adding: "I am a completely clean guy.

"I have never had the temptation of doing something wrong."

Nadal added: "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 drugs test but has been the subject of speculation that he dopes.

In 2011, former French Open champion Yannick Noah wrote a newspaper article saying Spanish sporting success was due to doping.

A year later, a satirical French TV show featured a life-size likeness of Nadal filling up his car's gas tank from his own bladder before being pulled over by traffic police for speeding.

Then in 2013, Belgian former professional player Christophe Rochus questioned Nadal being able to dominate the 2012 French Open and then be injured two weeks later at Wimbledon.

Nadal said he has taken advantage of some new treatments for his knee problems, like stem-cell therapy and Platelet Rich Plasma (PRP) therapy, often known as blood spinning.

Nadal speaks to the media in Indian Wells before the start of the BNP Paribas Open

"I have been open all my career," he said. "I never tried to hide nothing that I did. I did PRP and then I did stem cells.

"The first time with PRP it worked fantastic and the second time it was bad. I had to stop playing tennis for seven months.

"With stem cells, I used it two times on my knees and it worked very well. I am not doing, never did, and never going to do something wrong."

Nadal added that he trusts a doctor to monitor what medication he takes.

"He has been the doctor for all the Spanish players for a number of years," he said. "I would never take nothing that he doesn't know about."

Former world number one Sharapova announced on Monday that she failed a drug test at the Australian Open in January.

The five-time Grand Slam winner tested positive for meldonium, which was added to the World Anti-Doping Agency's banned list this year.

Nadal said Sharapova deserved to be punished as an example to others.

"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."

Have other players commented on Sharapova?

Yes, quite a few have been talking as they prepare to play in Indian Wells. This is what they've had to say:

Petra Kvitova: "Of course it's not great for her. It's something which we all should know, what we are taking and what we are putting into the body."

Agnieszka Radwanska: "A very sad day for tennis. We're in shock all of us. Nobody expected that for sure."

Svetlana Kuznetsova: "This strange mistake will not be able to outshine all of what she has achieved in tennis."

Novak Djokovic: "I feel for her with all that's happening and I just hope she gets out of this stronger."