The former Manchester United and Fiorentina striker expressed his outrage about the event on Twitter and insinuated that the result was fixed.
"I wonder how much they talked before the fight and planned it all out. Disgrace to sports," the Italian wrote.
"Please tell me when Floyd was rocked, why did the ref start talking to McGregor and help Floyd recover. Bulls**t man.
"I'm blaming the leaders of boxing that let this s**t be this big. No more morals."
Mayweather won the match after the referee brought it to a close in round 10 with McGregor showing signs of fatigue.