Floyd Mayweather's upcoming exhibition fight with Japanese kickboxing sensation Tenshin Nasukawa is a complete joke and is nothing but a money grab, according to Top Rank's CEO Bob Arum, who ripped Floyd for even taking the fight.

"It is a non-event. It is not a sporting event," Bob tells TMZ Sports.

Arum was out at Craig's this week when he made sure to stop for our photog, to crap all over Mayweather's highly-anticipated New Year's Eve exhibition in Japan.

"That's pretty much a joke, isn't it? I think so. I think so. Because, it's not a real fight ... the people who are watching that nonsense are pretty well jerks."

In fact ... Bob tells us he thinks the only reason the tilt is going down is because Mayweather needs the money.

"He needs money for Christmas and the New Year, and this is a good way for him to make some money. God knows Floyd always needs money," Mayweather said.

The contest will be fought over a three rounds with traditional boxing rules. Nasukawa is not allowed to kick or use any non-boxing moves. There will be no judges and no winner will be announced at the conclusion of the bout.

Arum promoted Mayweather for a good part of his career - until the undefeated 50-0 boxer broke away from Top Rank in 2006. Mayweather, 41-0, announced his retirement from the sport in August of 2017 - when he stopped UFC Conor McGregor in the tenth round of a cross-sport boxing match in Las Vegas. That was Mayweather's first contest in two years.