Roger Federer said only that he was surprised by Maria Sharapova's positive drug test. But when speaking in generalities, the Swiss star may have voiced more of an opinion.

Federer lamented tennis' inconsistent drug-testing measures in the wake of Sharapova's positive test for meldonium, The Guardian reported.

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"What is the right amount and what's not?" Federer asked, referring to the regularity of drug-testing. Clearly, I was very surprised [about Sharapova]; I thought she was going to announce her retirement. But it also shows that the famous players can get caught in the system."

When asked whether he thought the sport had a drug problem in general, Federer's answer was more pointed and direct.

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"I don't think so. Maybe I am naive in the fact that I believe athletes, I trust what they are doing. Clearly, when they get caught you turn because you are like: 'I can't believe that they tried to do that.'"

Sharapova's announcement and subsequent ban from the game, pending a ruling from the International Tennis Federation about a possible long-term suspension has created a rift in the tennis world between those who protest her test as an honest mistake and those who label her a cheater.

Federer believes more testing should be done to crack down on the issue in the sport.

"I still believe we should keep blood samples for 10 years, so athletes and tennis players know that's the case, that you could get punished retroactively," he said. "I'm a big believer in that.

"I've been in Dubai for 10 years now and I've been tested once in 10 years -- that's not OK for me. I get tested more in Switzerland because a tester lives in my village. He comes and sees me the day after my surgery and a week later.

"In Dubai they've come once because of the Asian games. I'd like it to be the same way and fair. Tennis is doing more and more. It was disappointing to say the least."

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