John Tomic denied a charge of assault against Thomas Drouet in a Saturday afternoon brawl outside a hotel where players in the Madrid Masters were staying, his lawyer Carmen Dieguez told journalists at a Madrid court.

The court set a May 14 hearing for a judge to decide his guilt or innocence.

"I don't feel guilty. I did not do anything wrong," John Tomic told reporters of the fight, which has sparked consternation in the tennis world.

John Tomic struck his son's training partner with his head only because his own arms were being held by Drouet and he had to protect himself from falling over, his lawyer said.

Tomic opted for a court hearing rather than paying a fine, she told reporters.

Bernard Tomic's father, who is also his coach, was arrested several hours after the fight in the central avenue Paseo de la Castellana and was jailed for a period before being released, police said earlier.

Tomic was expected  to face a judge later in the afternoon.

The Australian player and his father were in Spain for the Madrid Masters.

Todd Woodbridge, the head of men's tennis for Tennis Austraia, earlier confirmed that John Tomic was involved in an incident but said the details were as yet unclear.

"We're still trying to ascertain if or what charges have been laid," Woodbridge told Australian radio, without commenting on reports of the attack.

"What's important for us at Tennis Australia is that this allegation is thrown toward John, his dad, and not to Bernard."

In a statement, Tennis Australia said the allegations were "very concerning".

"We are working closely with ATP officials who are investigating the incident and are unable to comment further until the full facts are known," it said.

In France L'Equipe newspaper said Drouet, from Monaco, sustained a broken nose, stitches to a cut above his eye and bruising to the back of his neck, the paper said.

He then reported the incident to the police and John Tomic was later detained for questioning, it said.

L'Equipe quoted Bernard Tomic as saying that he had been with his physical trainer at the time of the incident and had seen or heard nothing.

"It's a very odd situation," he was quoted as saying by the paper. "I wanted to talk to Thomas, but he was in hospital. I haven't seen my father since then."

John Tomic rang an Australian journalist on Monday to confirm he was not in jail.

Tennis legend Wally Masur, meanwhile, told Sydney radio: "(John) is a pretty volatile character. He came from the Balkans, from a war-torn country, and came out (to Australia) with basically nothing," he told Sydney radio.

"You can't deny the fact that the reason that Bernie is a pretty good tennis player is that John has been behind the scenes driving him from a young age.

"I just can't understand why, when Bernard has had a lot of success and he's on a decent path and while he's got good people around him including Pat Rafter and the Davis Cup team, why John can't step away, why he feels this need to be so involved."

Bernard Tomic, currently ranked 49, last year created more headlines off the court than on it, including run-ins with police in his sports car and claims he was not trying hard enough.

The 20-year-old recently was recalled to Australia's Davis Cup team after captain Patrick Rafter disciplined him for a lack of professionalism following admissions that he gave less than full effort in matches at New York and Shanghai last year.

Tomic won both his singles matches and clinched victory for Australia in their Davis Cup Asia-Oceania Group One second-round tie against Uzbekistan last month.

But he has made a poor start to this year's European clay court season and in his latest match lost in straight sets to Czech veteran Radek Stepanek in the first round of the Madrid Masters.