And, the 3x Grammy award winner isn't alone ... lots of fans are pissed off at yet another controversial decision.

"I'm just letting y'all know I am done with boxing," the 48-year-old rapper said. "They will never get another motherf***ing dime out of me."

"This is a travesty! I am done with boxing!"

The highly contested fight went down Saturday night in Las Vegas ... and went the full 12-rounds. Two judges scored the fight 115-113 (7 rounds to 5), and the third judge had it 16-112 (8 rounds to 4).

Boxing star Shakur Stevenson is also of the belief that Loma was screwed, saying he scored it 8 rounds to 4 rounds.

"Lomachenko won," Stevenson said after the fight. "I thought it was robbery. Lomachenko won."

Of course, Team Loma also believes they were screwed ... and say they plan to appeal the decision to the Nevada State Athletic Commission.

"Somebody needs to end this injustice," Lomachenko’s manager Egis Klimas said during the post-fight press conference.

"Those judges’ scoring is completely insane, and they do not understand how those fighters are working hard to get into a place and to be robbed like that, it's not acceptable."

It's yet another controversy in the sport of boxing ... and it comes a week after a highly controversial stoppage in Rolly Romero and Ismael Barroso match.