A well-known sportsman, who is already under investigation for rape, is alleged to have forced another woman to carry out a sex act on him.
Gardaí are probing a complaint in relation to the alleged incident, which happened in a vehicle in the car park of a Dublin pub on Friday night.
Officers have received a complaint from a woman in her early 20s that she was forced into a sex act by the sports star after leaving the pub with him.
Senior sources say the sportsman and the young woman had been earlier socialising together with a group of people.
The "traumatised" woman made a complaint to gardaí on Saturday morning and a full investigation is under way.
The alleged victim's claims are being treated as "credible" but no arrests have yet been made.
The exact whereabouts of the sportsman were not known last night.
Gardaí have confirmed they are investigating the alleged sexual assault.
"Investigations are ongoing and no arrests have been made at this time. Owing to the nature of the investigation we will not be commenting further at this time," he added.
A team of specialist gardaí have been working on the case and it is expected they may interview the sportsman as early as this week.
Friday night's allegations are completely separate to a rape allegation the sportsman is facing, in which gardaí have sent a file to the DPP. The DPP has yet to make a decision on whether he should be charged with the offence.
The man was arrested in January in relation to the rape allegation and it is understood he claimed he had consensual sex with that woman.
A young woman alleged she was raped in a south Dublin hotel in the early hours of Monday, December 10.
Clothes belonging to the alleged victim were examined as part of the investigation.
She was treated at the Sexual Assault Treatment Unit at the Rotunda Hospital, leading officers to establish the allegation was credible.
Detectives at Pearse Street garda station spent almost two days investigating the allegations without finding an exact location of the attack.
However, as they followed lines of investigation, details emerged which led gardaí to move the focus of their investigation to the south Dublin area.
The report that was sent to the DPP includes statements from the woman and her alleged attacker about the incident, along with medical reports, witness statements and CCTV.
The DPP will decide whether there is enough evidence to charge the sports star.