Tennis legend John McEnroe has admitted to unknowingly taking steroids during his career, according to a report in The Daily Telegraph newspaper in Sydney on Monday.

"For six years I was unaware I was being given a form of steroid of the legal kind they used to give horses until they decided it was too strong even for horses," McEnroe, 43, said.

He didn't say who gave him the steroids.

The New Yorker also asked the ATP to appoint an independent commissioner to improve the image of men's tennis.

The sport is in crisis following Greg Rusedski's positive test to nandrolone.

"We have enough problems in the sport. It's the last thing we needed," McEnroe said.

McEnroe also urged the ATP to come down harshly on Rusedski or anyone else who tests positive for drugs.

"Watching him play, I've never noticed anything about him that struck me as different," he said. "But I don't know him that well.

"It would be surprising if it were true."