First reported by The Daily Mail, the allegations against the Penrith hooker suggest he brought a woman into camp on June 20, and again on the day of Game 2. The Blues were moved to Kingscliff on June 21 ahead of Game 2 at Suncorp Stadium with the COVID outbreak worsening in Sydney.
The publication also suggests Koroisau was preparing to bring the woman into camp for a third time ahead of the series dead rubber, only to change his mind when it was announced Jai Arrow had been removed from the third game and fined for his own biosecurity breach.
Arrow was fined $35,000 for his breach, while also being forced to undergo a mandatory 14-day quarantine period.
The strict NRL bubble, which now exists for all NRL teams upon their move to Queensland, means no one from outside the playing group or their families is allowed to have contact with those listed in the bubble.
The woman was not Koroisau's partner, according to the publication, who have obtained text messages.
The Sydney Morning Herald are now reporting that the NRL is aware of the potential problem, and the integrity unit are investigating.
Koroisau served as 18th man during the first two games of the series, before moving into the bench utility role during the third game due to injuries of Penrith teammates Nathan Cleary and Jarome Luai. It forced Jack Wighton to start, opening the spot for the 29-year-old to make his Origin debut.
The NRL, NSWRL or Penrith Panthers are yet to provide official comments on the reported breach.