Conor McGregor had a drink thrown over him after he sang a Celtic song in Glasgow.
McGregor, who lost in his professional boxing debut to Floyd Mayweather in August, was in Glasgow as part of an 'Evening with Conor McGregor' event.
"What's up Glasgow Celtic?" McGregor cried as he addressed fans in a nightclub after the appearance.
"The only football club around here we're talking about. Glasgow is green and white!
"Where's Rangers at?" shouted McGregor. "There's only one team in Glasgow. There's only one team in Glasgow. Walking along, singing a song, walking in a Celtic wonderland."
McGregor's Celtic song prompted one fan - presumably Rangers-supporting - to throw their drink at the 29-year-old.
The UFC icon recently revealed he would have been fined $10m if he had been disqualified in his Las Vegas bout with Floyd Mayweather earlier this summer.
"Here's when I knew I was up against it: The ref was like, even if I lift my leg up, it's a point deduction. I'm like, "How is that a point deduction without even a warning?" he said during his appearance at the Glasgow event.
"So they're telling me they're going to deduct points straight off the bat. And if I do get disqualified for any reason, it was a $10million fine. Ten million f***ing dollars."
McGregor is expected to return to the octagon for his next competitive bout, with a third rematch against Nate Diaz rumoured to be in the offing.