While the fight is happening, no one knows exactly what rules will be in place as they did not announce whether they would be boxing or kickboxing - his Instagram picture shows him wearing a boxing glove and an MMA glove.
Former five-weight world champion Mayweather beat UFC's Conor McGregor in a boxing match in August 2017 to extend his ideal record to 50 wins.
In an interview on Saturday, the 41-year-old said he would be comfortable fighting under any format.More news: Order to kill Jamal Khashoggi came 'from the very top'
Mayweather, who makes it a point to regularly bring up how much money he will make for his fights, did not discuss his pay for the event. "I look forward to giving you guys entertainment come December 31, but my relationship with Rizin doesn't just stop here".
Boxing superstar Floyd Mayweather is once again coming out of retirement, but this time, it could be as a mixed martial artist. I'm a little surprised myself.
Mayweather had said in September that he was coming out of retirement for another fight with Manny Pacquiao after the two of them had been pictured talking at a music festival in Japan. "As a professional I haven't had a chance to go outside the U.S.to display my skills and to display my talent for the world".
Nasukawa competes in RIZIN championships in both MMA and pure kickboxing. Nobody has defeated my opponent in the past and I would like to be the man who makes history.More news: Devin McCourty’s Pick-6 Seals Patriots’ 25-6 Win Over Bills
"As far as the weight class and the rules, we'll get that situated in the next few weeks", Mayweather said. It's not out of the realm of possibility that the bout is fought under kickboxing rules.
Ariel Helwani said tonight that the rules and weight still had to be worked out. While the organizations were initially meant to co-exist independently with occasional crossover events, the UFC instead absorbed many of Pride's top fighters before folding the operation.
Regardless of the final rules of the bout, the move makes a potential rematch with McGregor or a fight against Nurmagomedov much more likely than it felt just days ago.More news: Michael Cohen Claims Trump Made Several Racist Comments Before 2016