The former five-weight world boxing champion appeared at a press conference to reveal a fight against the Japanese fighter on December 31 in Tokyo, but the 41-year-old took to social media on Wednesday to address the issue.
Mayweather wrote: "First and foremost, I want it to be clear that I, Floyd Mayweather, never agreed to an official bout with Tenshin Nasukawa."
Mayweather, who retired with a perfect professional boxing record of 50-0 after defeating UFC star Conor McGregor in August last year, did not confirm whether an "exhibition" would still go ahead.
He added: "I was asked to participate in a nine-minute exhibition of three rounds with an opponent.
"This was to be an exhibition put on for a small group of wealthy spectators for a very large fee.
"This exhibition was previously arranged purely for entertainment purposes with no intentions of being represented as an official fight card nor televised worldwide.
"I want to sincerely apologise to my fans for the very misleading information."
Mayweather, widely regarded as the greatest boxer of his generation, appeared to have confirmed the fight against Nasukawa would take place earlier in the week.
Speaking at a press conference to promote MMA promotion company Rizin Fighting Federation, he said: "I wanted to do something different. It doesn't matter where the fight is but it's in a special place.
"I always wanted to display my skills outside the US and be in a special fight. This presented itself, I spoke with my team, I got with Rizin and we put it together."
Mayweather, reported to have earned £228million from his fight with McGregor, said he had not heard of Nasukawa until his recent trip to Japan.
Nasukawa, 20, is unbeaten in 27 kickboxing fights and holds a 4-0 record in mixed martial arts.
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