Novak Djokovic and Andy Murray share a respectful rivalry that dates back to their junior days.

But they don't share common views on doping.

Becker: Murray Out of Order on Doping

"I have played against players and thought, 'They don't seem to be getting tired.' " Murray told the Sunday Daily Mail. "Have I ever been suspicious of someone? Yeah. You hear things."

While Murray suspects doping exists on the pro tour, Djokovic insists the sport is clean.

The world No. 1 shot down Murray's suggestion and said he's already told the second-ranked Scot he doesn't agree with his statement.

"I don’t share Andy’s concerns," Djokovic told the media in Berlin after receiving his second straight Laureus World Sportsman of the Year award. "As long as we don’t have proof that the game isn’t clean, then it is clean. I’ve read what he said, I have great relationship with Andy, I’ve spoken to him and he didn’t mean specific individuals."

Djokovic's comments support his coach Boris Becker's belief that "tennis is clean."

'It's a very dangerous subject. I can only repeat that tennis is clean," Becker told the media at the Laureus World Sports Awards in Berlin. "I believe 100 percent Andy is clean. Roger is clean, Rafa (Nadal) is clean, Stan (Wawrinka) is clean, all these guys are clean...

"Rumors are not reality. Tennis is an Olympic sport. All the top guys, I know for a fact, get tested a lot. Everybody is clean and so we can't spread rumors. If Murray feels that he lost a match because the other guy was running longer than him it's because of the fitness, otherwise we would have known. [Murray] is one of the fittest players on the tour, he is very dedicated, puts a lot of effort into his training and so are the others."

This isn't the first time the world's top two have disagreed on a doping issue. After fellow Head endorser Maria Sharapova admitted testing positive for the banned drug meldonium at the Australian Open, Djokovic supported the five-time Grand Slam champion and suggested "it can happen to many players."

"I do feel that we all have to agree that (Maria) has been humble and responsible and brave in this process," Djokovic said. "To come out with that, it's not an easy thing. To face so much media and so much attention from the world of sport and also other fields of life and carry that on your back, it's something that you must admire and respect.

"Of course I was saying that it can happen to anybody if she didn't know that it was on a forbidden list. Now I'm saying in that scenario it can happen to many players, because I can assure you that many players don't look in those e-mails."

Murray, who has long been a proponent of more transparency in tennis' drug-testing policy, took a harder line stance saying any player taking a drug without a medical reason is using the substance as a PED. 

"It’s not up to me to decide the punishment, but if you’re taking performance enhancing drugs and you fail a drug test, you have to get suspended," Murray said. "I think taking a prescription drug that you don’t necessarily need, but just because it’s legal, that’s wrong, clearly. That’s wrong.

"If you’re taking a prescription drug and you’re not using it for what that drug was meant for, then you don’t need it, so you’re just using it for the performance enhancing benefits that drug is giving you. And I don’t think that that’s right."

Photo credit: Tom Dulat/Getty Images for Laureus