Transparency is on Rafael Nadal's side.

The 14-time Grand Slam tennis champion has denied allegations that the stem-cell treatment he is undergoing for his back is a form of illegal doping.

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According to reports, fans and analysts have questioned the legality of the procedure, prompting Nadal to speak to El Mundo about his condition.

"I don't think it's like that," Nadal told El Mundo about the doping allegations against him. "I don't know the exact details of treatment procedure but the thing is that it's being done in line with the international rules. I only do what is allowed and I have never imagined of doing something that is wrong."

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Other athletic stars, including NBA icon Kobe Bryant of the Los Angeles Lakers, have undergone similar procedures in the past without accusation.

Nadal was forced to withdraw from the ATP World Tour Final to have appendectomy surgery after playing the previous month with appendicitis. He elected to have the stem-cell treatment on a back that has bothered him since his five-set loss to Stan Wawrinka in the Australian Open final in January.

Latinpost.com added that Nadal said doctors took out blood from him and spun it in a centrifuge to get the growth factor in it before it was re-injected to help his body regenerate tissues on his ailing back.

"After the procedure, Nadal said that he has been feeling better than before, which makes him believe that he will be back to his deadly form when the new season starts," latinpost.com reported.

Nadal never hid the fact that he was going to have the stem-cell treatment, so accusations of doping in connection to the treament are unclear.

Nadal originally faced a doping allegation from Christophe Rochus after the Australian Open Final. Rochus, who served as a commentator for Sport Euro's Australian Open coverage, accused Nadal of faking his back injury during his finals match against Stan Wawrinka and going to the locker room to get a "shot."

"When he returned from the locker room he was limping. Then, surprisingly, he could run in the third and fourth set. Clearly left the track to get a shot," Rochus said, according to au.ibtimes.com.

Those comments put Rochus under fire, au.ibtimes.com reported, and Rochus tried to explain his comments but maintained his accusation that Nadal took a shot in the locker room.

Rochus also raised the issue with Nadal in 2010, according to the report.

"When one can afford good doctors to do personal research, it is possible to take undetectable drugs. So in my opinion, anti-doping controls are useless and they really don't prove anything. Regarding Nadal, those rumors are rumors even if everyone has the same question: How can you be so strong in Roland Garros and one month later, you are apparently unable to play? That's why it looks so suspicious, but we have no proof. Maybe he really is injured," Rochus said.

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