Rafael Nadal believes Maria Sharapova deserves to be punished after failing a drug test at the Australian Open.
The former world No 1 was found to have taken meldonium - a drug known to increase endurance capabilities - which was prohibited from January 1 this year.
Sharapova has been provisionally suspended from March 12, but Nadal insists she 'must pay' for failing to take notice of new doping regulations.
"It is difficult to imagine that something like this can happen, but mistakes happen," he said ahead of his first round match at Indian Wells. "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."
Nadal, who enters this week's tournament as the No 4 seed, says he has never been tempted to take a performing enhancing drug and wants to continue to be a role model for young players.
"I am a completely clean guy,' he added. 'I have never had the temptation of doing something wrong."
"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."
Speaking at a press conference in Los Angeles on Monday, Sharapova conceded that she had received a notification from the International Tennis Federation on December 22 to say that meldonium was being outlawed. She admitted that she did not follow an information link that was provided.
"I had legally been taking this for 10 years," she said.
"I take responsibility for my professionalism in my job and I made a big mistake. I know there will be consequences and I don't want to end my career this way. I really hope I will be given another chance to play tennis again. I can't blame anyone but myself. I have let my fans down."
"I know many of you thought I was retiring but if I was ever going to announce my retirement it would probably not be in a downtown Lost Angeles hotel with this fairly ugly carpet."
"It made me healthy and that is why I continued to take it," Sharapova said of the banned substance after taking a small number of questions from the floor.
"I am still working through my injury and that is the reason I withdrew from Palm Springs, because I have still not healed my injury.
Asked if she knew what the consequences of her failed test may be, Sharapova added: "I do not. This is very new for me, I just received the letter a few days ago and I will be working with the ITF."