Floyd Mayweather Jr. had one of his cars set alight as he visited Birmingham as part of his ongoing UK tour.
The retired undefeated boxer made an appearance at the Birmingham ICC on Saturday, where he conducted a Q&A and watched Tony Bellew's shock defeat of David Haye.
He spoke of his admiration for British boxing fans, but outside the Midlands venue a people carrier, branded with The Money Team insignia, was torched.
"Police are investigating an arson attack on a vehicle parked at a Birmingham hotel," a West Midlands Police statement read.
"No-one was injured following the fire at 0330hrs this morning [Sunday 5 March] at the Park Regis Hotel in Broad Street.
"Offenders smashed the window of the vehicle, a people carrier, before pouring accelerant inside and setting it alight.
"Enquiries into the fire, which caused extensive damage to the vehicle belonging to a guest, are currently on-going and police are examining CCTV from the area.
"Anyone with information is asked to call police on 101."
Mayweather Jr., who is due to appear in London on Monday night, had earlier paid tribute to his UK fans, revealing it was a regret that he never fought in Britain.
"I represented the U.S. in the Olympics, I love my country. But the U.S. fans will love you on Monday, if you lose they'll hate you on Tuesday, if you win it will be back to loving you on Wednesday," he is quoted as saying by The Telegraph.
"The thing about these UK fans is if they are with you, they're with you. I've got calls from Africa, all around the world, to do a tour, but I said the UK fans first, always.
"These fans have been loyal and paid hard-earned money to come out there and support me."
Mayweather Jr. has recently been linked with a return to the ring to face UFC star Conor McGregor, and he again hinted that he was prepared to take the fight.
"If Conor McGregor really wants to fight me, we can make it happen," he said. "But is he blowing smoke up everybody's ass?
"In one fight I made more than Conor McGregor has made in his whole career. The difference between me and him is this: He has to fight.
"If I was him and I was smart, before I lose again in the UFC, I'd let Floyd Mayweather kick my ass for a lot of money. It makes business sense."