Ciryl Gane's apartment was robbed while the heavyweight was fighting at UFC Paris on Saturday.
The Frenchman stopped Serghei Spivac in front of home fans at the Accor Arena.
But the 33-year-old Gane's home in Paris was broken into by thieves while he was at the event.
He is among several French athletes to be targeted in recent months, with Italy and PSG goalkeeper Gianluigi Donnarumma attacked and robbed at his home in July.
French police and Gane's team declined to comment on the incident when approached by BBC Sport.
But French outlet Le Parisien claim £130,00 worth of goods including a Rolex watch were stolen from Gane's home and police were alerted to the incident at 07:30 BST on Sunday.
Gane is one of the best heavyweights in the world and was fighting in the UFC for the first time since losing to Jon Jones in a title fight in March.
He was the main event in Paris, making short work of Moldova's Spivac, beating him inside two rounds.
Gane was one of seven French fighters to pick up a win on home soil.