Irish police are aware of claims McGregor allegedly assaulted a man with ties to Kinahan lieutenant Graham "The Wig" Whelan — one of the country's most feared gangsters who was a key player in a long-running feud which claimed 16 lives in the early 2000s.
One report suggested the man, who is in his 50s, is Whelan's father.
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McGregor was at the Black Forge Inn in Crumlin, the Dublin suburb he grew up in, when he is alleged to have thrown several punches after a dispute with a group of men on Sunday night local time.
McGregor is alleged to have tried to strike one member of the group before the associate of Whelan's stepped in and was punched twice by the UFC star.
The reports claim McGregor also punched a third man during the incident before he was escorted out of the pub and into a car.
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Williams has described those involved as "psychotic thugs for whom there are no boundaries or behavioral parameters".
He writes: "if you cross them they will either kill you, seriously injure you or simply leave you and your loved ones living in fear of your lives.
"Over the past 72 hours sources in the criminal underworld and the gardai (police) have been consumed by this developing and chilling saga."
