Rabbi Moshe Gutnick, who heads the Organisation of Rabbis of Australasia, said he received an anonymous phone call from a boy more than 20 years ago about the alleged abuse at Sydney's Yeshiva.

Rabbi Gutnick, who was based in Strathfield in Sydney's west at the time, said he alerted senior members of the Yeshiva about the boy's allegations, but did not contact police.

''Knowing what I know now, I would have probably called the police,'' he said.

Fairfax Media has also learnt of more child sexual abuse allegations at Bondi's Yeshiva College in 2003.

The alleged abuser of the boy who contacted Rabbi Gutnick, and a male teacher accused of indecently assaulting a 12-year-old Yeshiva student at a camp in 2003, were both relocated overseas after complaints were made about them.

Fairfax Media does not suggest the Yeshiva community played any role in the men leaving the country.

The victim of the 2003 incident, who spoke on condition of anonymity, said his family reported the incident to the NSW Department of Community Services and to two principals at Yeshiva College.

The victim said he was dismayed to learn that the accused teacher was flown overseas within weeks of his complaint. ''How would anyone know if he went on to do the same thing there?'' he said.

A source connected with Yeshiva said the college also reported the 2003 incident to child protection services.

Rabbi Gutnick said a man, claiming to be the same boy from 20 years ago, contacted him in 2011. The rabbi said he urged the man to contact police.

Fairfax Media last month reported that the man accused of the 1980s sexual assaults on at least four victims, including the boy who contacted Rabbi Gutnick, was being investigated by NSW Police.

The alleged abuser told one of his victims in a recent conversation that he was called to the office of the Yeshiva Centre's spiritual leader, Rabbi Pinchus Feldman.

''He [Rabbi Feldman] just told me it shouldn't happen and I should take steps to avoid it,'' the accused man told his alleged victim. ''It was a once-off conversation in his office.''

The Yeshiva Centre last week released a statement on behalf of Rabbi Feldman, who is Rabbi Gutnick's brother-in-law, saying he had no recollection of any confession of child sexual abuse 25 years ago.

In response to a series of questions last week, the Yeshiva Centre said in a statement: ''Yeshiva treats its child welfare responsibilities with the utmost care and has always endeavoured to comply in full with all its legal and moral child safety obligations. It is our policy to consult with appropriate government authorities about such matters.

''Yeshiva representatives recently initiated a high-level meeting with the police to discuss an investigation into historical allegations of child abuse. The police have informed Yeshiva representatives that media speculation could endanger the success of their investigation.

''The police have requested that Yeshiva refer all inquiries relating to the investigation directly to them. It is therefore inappropriate for us to comment on any of these matters.''

Manny Waks, a Melbourne advocate for child sex abuse victims, commended Rabbi Gutnick's admissions.