You can see by the way UFC president Dana White deliberately keeps his speech to an absolute minimum how bad for business he thinks it is.
McGregor's tardiness - he arrived two hours late - wasn't ideal either. Not that Mayweather was bothered. "I don't really worry about that," Mayweather said. "It's all about being a professional."
After attempting, some might say unsuccessfully, to go toe-to-toe with McGregor on a theatrical level earlier in the promotion, Mayweather, 40, took a more stoic, elder statesman-like approach to his final sound-off.
He offered extended tributes to all the major parties involved in putting the fight on, thanked his family and was also respectful to White and McGregor.
But he was committed to making two points: His experience in boxing is unparalleled and he's subdued countless heavy hitters who came in planning to knock his head off.
Who did it: McGregor v Mayweather
"Anything and everything that can be done in boxing, I've done it," he said. "Not just once, not just twice ... 1000 times."
"A lot of times you've got guys talking about what they're going to do, what they're going to give, how they're going to be aggressive," Mayweather added. "But you also have to realise, there's two sides to everything. The same way you're talking about giving it, hopefully you're able to take it also."
McGregor wasn't his usual flamboyant self, which also isn't a bad sign if it's an indication of him locking in on Sunday's rumble. "It's a lot more subdued, a lot more business-like, which is the way I like it," the Irishman noted of proceedings. "Sometimes."
McGregor reasserted his belief Mayweather made a big mistake in agreeing to wear eight ounce gloves rather than the standard 10 ounce gloves.
"I will go forward and I will break this old man," he said. "Eight ounce gloves - he made a big, big error I feel.
"I will beat this man at his own game. I am on a different level to him.
"You should have kept your mouth shut, you should have left me where I was. He is not even a quarter of the man I am.
"I'm gonna f*** this boy up. Make no mistake, he should have left me where I was."
"The Notorious" was distracted by heckling a couple of times and went a little off track while discussing an unformed plan to introduce his own type of hybrid fighting cage.
"I was actually thinking about maybe going forward - since I'm the king of the boxing ring and the king of the Octagon already - when I've conquered both maybe I might just create my own hybrid of a boxing ring and an Octagon," McGregor said.
It certainly wasn't one of his best delivered lines but there were a couple of treats for fight fans regarding his future: He plans to compete in boxing and MMA.
"I'm an active fighter," McGregor said. "I enjoy it. I don't stop thinking about fighting. So when this one is done I'll have about 20 seconds where I relish in victory and then think who's next?"
