Andy Murray's suspicions of performance-enhancing drugs in tennis have been labelled "totally out of order" by Boris Becker, who insisted all the top players are clean.

World number two Murray claimed in an interview on Sunday that he suspected some of his opponents may have doped in the past, in the wake of Maria Sharapova's drugs ban.

Becker - coach of world number one Novak Djokovic - reacted angrily to Murray's comments, rejecting the outspoken two-time grand-slam champion's stance.

"We have random drug testing and unless it's proven, they are 100 per cent innocent," the three-time Wimbledon champion 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."

Becker added: "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.

"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."