A former Tennis NSW coach devastated a promising teenage player through verbal abuse, lewd jokes, touching and sexual advances, a royal commission has heard.

But after a different coach told the organisation Noel Callaghan was making derogatory sexual remarks about the girl "sleeping around", he received the state top's coaching job.

The player's mother said a Tennis NSW investigation appeared an attempt to discredit her daughter, who disappeared for weeks after a "demeaning and hurtful" interview with officials.

Mr Callaghan, a former coach to professional players such as Sam Stosur, denies all allegations of wrongdoing.

The girl, known by the pseudonym BXJ, began private lessons with him in 1995 when she was 14. "She was fiercely competitive and a perfectionist," the player's mother told the Royal Commission into Institutional Responses to Child Sexual Abuse on Friday. "She always said she wanted to play at Wimbledon."

But when BXJ was 16 years old, Mr Callaghan allegedly began telling her rude jokes and asking her about her sex life.

The player's mother said her daughter told her Mr Callaghan had touched her on her breast and thigh on separate occasions in 1997.

Mr Callaghan allegedly tried to have sex with the girl while on a Sydney University tennis camp during the same period. "He sat astride her on the bed, straddling her," BXJ's mother said. "He told her he would be back the next night."

BXJ ceased coaching with Mr Callaghan in 1998. She disclosed the alleged abuse to her new coach, BXD, who said she herself had been abused while a pupil of Mr Callaghan's.

An investigation found BXJ was more likely than not telling the truth but a second legal opinion found it would be "unwise" to dismiss Mr Callaghan without giving him a chance to respond to the allegations.

BXJ was eventually told to take her allegations either to the Equal Opportunity Tribunal or the NSW Police.

"The decision by Tennis NSW to do nothing very much defeated her," the player's mother said. "It has eaten away at her ever since."

The mother said BXJ developed ongoing depression, drug dependency and an eating disorder, leaving her unable to work.

She said criminal charges laid by her daughter were dismissed because she was too ill to proceed but Mr Callaghan's lawyer said a lack of evidence had prompted that decision.

Indecent assault charges against Mr Callaghan relating to another player were dismissed in 2002. The following year Mr Callaghan was found not guilty of sexually assaulting BXD.

Another witness at the commission, former NSW assistant coach Amanda Chaplin, said she had seen Mr Callaghan take a "quite different approach" with these two players.

"They would often be sitting up in the cabana and not hitting a lot of tennis balls," Ms Chaplin said. "He would often be up close and it looked intimate."

Ms Chaplin said she told the then chief executive of Tennis NSW, Craig Watson, about derogatory remarks Mr Callaghan had made about BXJ.

He was promoted to state coach a short time later.

Mr Watson told the commission Tennis NSW had initially waited for BXJ herself to make a complaint before taking action.

Commissioner Peter McClellan asked if it was appropriate to wait for an alleged victim to complain when that victim was a child.

"With the benefit of hindsight, possibly not, no, not," Mr Watson said. He said "on reflection" that some of the questions BXJ was asked by a lawyer during the investigation were inappropriate.

Ms Chaplin said after she made the allegation she suffered a campaign of "disgraceful victimisation" by friends of the Callaghans and even heard Mr Callaghan's wife had made a death threat.

As of February, Mr Callaghan was the head coach in the Australian Tennis Academy at Hope Island in Queensland. He is overseas and not set to give evidence.

"He has always denied the allegations," his lawyer Aaron Kernaghan said outside the commission headquarters.