Apparently McGregor was passing out cups to patrons at a bar called the Marble Arch in Dublin, in April, and encountered this guy who declined his drink offer. This rejection rubbed McGregor the wrong way, as you can see what looks like McGregor sucker punch the guy before being carried out.
An official from Ireland's national police force released a statement to the MMA Junkie that reads:
"Garda are investigating an assault incident that occurred at a public house in Drimnagh, Dublin 12, on 6/4/19 at approximately 2:30pm. Investigations ongoing in relation to this incident and no arrests have been made to date," the statement reads.