He has boxing training, but has never faced anyone with the speed of Mayweather.
Former multi-division world champion Mayweather fought and defeated wrestling giant Big Show in a No Disqualification wrestling match at Wrestlemania XXIV in March 2008. He needs just one more victory to surpass the record of the great Rocky Marciano and has been sent to the canvas just once in his career, in a fight he came back to win.
Mayweather Promotions will publicize the event, which will be available on Showtime pay-per-view.
In the 12 hours after the fight, Betfair Exchange saw £135k bet on the contest, which UFC president Dana White has described as "the biggest fight ever".
The 40-year-old Mayweather announced his retirement after beating Andre Berto also in Las Vegas in September 2015.
We're only hours into this completely bonkers saga and I think it's fair to say that it's already delivering on every possible level. His fight before that, a decision win over Pacquiao, was the richest in boxing history and reportedly made him more than $200 million. However, experience is clearly on his side in this fight as his opponent has never had a professional boxing match.
Famed for his granite chin and ability to keep coming forward, he has sparred countless rounds with the brash McGregor, who went on to become UFC champion at both featherweight and lightweight and is as well known for his trash talk as for his fighting skills.
Even if the actual bout may not shape up as a great matchup, the run-up to the fight will.
Interest in the fight has been incredibly high, with extraordinary numbers being bet in the hours immediately after Mayweather confirmed the fight by posting a short promotional video to his official Instagram page.