Floyd Mayweather directed a homophobic slur at Conor McGregor after accusing him of making racist comments during the media tour to promote their Las Vegas fight.
Former five-weight boxing world champion Mayweather will face UFC lightweight title-holder McGregor in 12 rounds under boxing rules in August.
“He called black people ‘monkeys’,” said the American, 40, during a news conference at Wembley Arena on Friday.
Then, once the pair entered a boxing ring at the event for the official promotion, Mayweather addressed McGregor as: “You punk. You faggot. You ho.”
The two men have conducted a series of news conferences in recent days to promote the fight, with stops in Los Angeles and Toronto before the trips to New York and London.
The 29-year-old Irishman has attracted criticism for a series of comments during those events and is alleged to have made racist comments during the third stop of the tour in New York on Thursday.
“He totally disrespected black women,” added Mayweather. “Then he spoke disrespectfully to my mother and he spoke disrespectfully to my daughter.”
The American added on Friday: “Racism still exists. I’m not going to stoop that low and speak about his like or speak about his child. I’m glad that he just had a healthy child and he has a beautiful family.”
Responding to Mayweather at the New York press conference on Thursday, McGregor said: “I’m a multicultural individual and I don’t have any ill feelings towards anyone. I don’t even see colour.”
Then, speaking to BBC Sport after the London event, he said: “I know who I am, people around me know who I am. We know his history, but I didn’t bring it up. The fight game is ruthless and it’s what I expect.”
In 2010, Mayweather made racist and homophobic remarks towards Filipino boxer Manny Pacquiao in a video posted on the website Ustream.