The MMA fighter who made his professional boxing debut against Floyd Mayweather Jr. in 2017 was Conor McGregor. McGregor, the former UFC lightweight champion, crossed over from mixed martial arts to face Mayweather in a highly anticipated boxing match on August 26, 2017, at the T-Mobile Arena in Las Vegas. Mayweather ultimately won the match by TKO in the 10th round, extending his undefeated boxing record to 50-0.