UFC President Dana White says that any possible (it's not possible) fight between Floyd Mayweather and Conor McGregor, even in a boxing ring under boxing rules, would have to go through UFC, as McGregor is a contracted UFC fighter.
McGregor being a contracted UFC fighter is one of the main reasons that this is not going to happen, but here we are, talking about it anyway. White also says that if Floyd really wants to do that circus act novelty event, where he would toy with and embarrass McGregor before knocking him out, he can contact him any time:
"We haven't talked about it. Conor McGregor's under contract with the UFC," White said. "If Floyd wants to fight Conor—call me, Floyd."
Mayweather (49-0, 26 KO) "retired" after his win last September over Andre Berto, but the feeling is that he's going to fight again, at least once more, after having his company seek trademarks for "TBE50" and "TMT50." Well, the feeling was he'd fight again well before he sought those trademarks, but you know what I'm saying. A recent interview on Showtime with Jim Gray also indicated that Mayweather is open to a return as long as he makes a nine-figure payday, and Floyd has said he's already spoken with CBS and Showtime.
McGregor (19-3 in MMA) is coming off of a loss to Nate Diaz on March 5, and isn't a boxer. He's had a very public spat with UFC recently, too, announcing his own retirement, which no one really took seriously, and apparently is off, or isn't -- who cares? This fight with Mayweather is not happening, and even if it did, it would be a farcical mismatch. Andre Berto and Robert Guerrero, two guys Mayweather has beaten with ease in the last three years, would also clown McGregor in a boxing match. This whole thing is ridiculous and has no chance of actually occurring.