The Comptroller and Auditor General has told the Disclosures Tribunal the former Garda Commissioner Martin Callinan told him there were allegations of sexual offences against Maurice McCabe.
The tribunal is investigating if senior gardaí made allegations to discredit and smear the garda whistleblower.
The job of the Comptroller and Auditor General (C&AG) is to make sure public funds and resources are used in accordance with the law and managed to good effect.
In 2012, the C&AG Seamus McCarthy began looking into allegations that penalty points had been illegally and corruptly cancelled by gardaí.
By January 2014, he was due to attend a Public Accounts Committee in Leinster House, where he told the Disclosures Tribunal the then-Garda Commissioner Martin Callinan approached him.
He said Mr Callinan told him garda whistleblower Sargeant Maurice McCabe was not to be trusted, had questions to answer and there were allegations of sexual offences against him.
Seamus McCarthy said he was surprised and did not tell anyone what had happened.
He said he appreciates that Martin Callinan denies that he said anything about these allegations.