Boris Becker insists tennis is clean following Andy Murray's "out of order" comments

Maria Sharapova is the latest high profile athlete who has been embroiled in a doping scandal

Boris Becker insists that tennis is a clean sport and branded Andy Murray's claims otherwise as "out of order".

Murray aired his suspicions over the use of performance enhancing drugs in tennis, but Becker insists that the sport's top players operate without doping.

"We have random drug testing and unless it’s proven, they are 100 per cent innocent," he told the Daily Mail.

"So to throw in a curve ball and assume something because somebody has won a Grand Slam or is fitter I think is totally out of order.

"Andy is one of the fittest players on the tour – he often outlasts other players and nobody is questioning his ethics.”

 "It’s a very dangerous subject. I can only repeat that tennis is clean. I believe 100 per cent Andy is clean.

"Roger [Federer] is clean, Rafael [Nadal] is clean, Stan [Wawrinka] is clean, all these guys are clean."

Nadal, who beat Murray this weekend en route to victory in the Monte Carlo Masters, has threatened to sue a former French government minister who accused him of using PEDs.

"There was always a suspicion of Rafa and I find that so unbelievably disrespectful about one of greatest players of all time.

"I can only speak for Novak and believe me he gets tested a lot! That can mean twice in a Grand Slam.

"In Melbourne he got tested in the first week and the second week. He would be playing a match at night and somebody comes to his hotel room at 7am to do a urine test and I think, ‘how dare you’. But those are the rules."

Maria Sharapova became the latest high profile athlete to become embroiled in a doping scandal after she admitted to use of a banned substance meldonium.

Maria Sharapova speaks during a news conference in Los Angeles. Sharapova says she has failed a drug test at the Australian Open. Image: Damian Dovarganes / AP/Press Association Images

Speaking in an interview with the newspaper Murray said: "I have played against players and thought, 'They won't go away' or 'They don't seem to be getting tired'.

"Have I ever been suspicious of someone? Yeah. You hear things.

"It's harder to tell in our sport as people can make big improvements to a stroke or start serving better because they have made technical changes.

"If it's purely physical and you're watching someone playing six-hour matches over and over and showing no signs of being tired, you'd look at that."