Mayweather posted to Instagram teasing the New Year's Eve bout.
Retired boxer Floyd Mayweather announced Monday in Tokyo that he will fight in the Rizin Fighting Federation, reports ESPN.
Mayweather will fight Tenshin Nasukawa on Dec. 31 at the Saitama Super Arena in Saitama, Japan. The two were introduced at the news conference in Tokyo.
Before the announcement, Mayweather posted on Instagram teasing New Year's Eve.
It's unclear whether the fight will be a boxing match or an MMA fight. Promoters are still working on the rule set, according to ESPN.
The 41-year-old Mayweather is 50–0, while the 20-year-old Nasukawa is also undefeated.
Mayweather said last month that he was interested in a potential showdown against Khabib Nurmagomedov, who challenged Mayweather to a battle of undefeated fighters after his own defeat of Conor McGregor. A messy post-fight brawl broke out between members of both McGregor and Nurmagomedov's entourages. But UFC President Dana White didn't think a fight between Nurmagomedov and Mayweather would happen. White said the crossover event would need to take place in an octagon if it did.
Mayweather also announced in September that he would come out of retirement to fight Manny Pacquiao. The two last fought in 2015, but there hasn't been any update to a possible rematch between the two.
Mayweather came out of retirement in 2017 to fight McGregor.