John Locher/Associated Press

While Floyd Mayweather Jr. spent most of his afternoon in a more subdued state, Conor McGregor remained boisterous Wednesday in the final press conference before their bout in Las Vegas on Saturday.

"I will break this old man...I don't see him lasting two rounds," McGregor said (Warning: link contains NSFW language). "I feel I'll have the decision to end it inside one. He messed up with them eight-ounce gloves.

"I'm gonna f--k this boy up, make no mistake. And when it's all said and done, I'm gonna feel a little bit sad. Because you all should have kept your mouths shut. You should have left me over in that other game where I'm from, that more ruthless game where we bounce heads off the canvas and drill them into the floor. You should have left me where I was because this man is not on my level, he's not even a quarter of the man I am."

McGregor, 29, will be making his professional boxing debut Saturday. He's the only UFC fighter in history to hold multiple championships simultaneously.

Mayweather, 40, is one of the most decorated boxers in history. This will be his 50th professional fight and will give him a chance to move to 50-0, breaking a tie with Rocky Marciano.

"Competing against the best, that's what it's about," Mayweather said. "Taking chances. What city better than Las Vegas to take a chance? This city is built on gambling, and I'm taking a gamble but it's worth it."

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Mayweather may be preparing to bet on himself in more than one way. Gambling expert RJ Bell reported Mayweather was considering a $5 million bet on himself. When asked, McGregor said he "may" bet on himself, but used the question as an opportunity to rip Money's penchant for gambling:

"I think he has a big-time gambling problem. From seeing him, he gambles on halftimes and things like that. He shows what his wins are but never shows what the losses are. Maybe that's why he's in the position he's in and had to take this fight."

While McGregor was quick to say he'd take care of business early, Mayweather made it clear he's confident in his ability to outbox his opponent.

"Pacquiao got bombs, Canelo got bombs, Shane Mosely had bombs, and all of those guys are going into the Hall of Fame," Mayweather said. "But one thing about me, I've got a grinning chin. The same way you give it, you have to be able to take it. Remember this."

McGregor, undeterred as ever, did not seem remotely phased by the difference in experience.

"The fight business is the fight business," McGregor. "I can go into any rule sets, that's what a true material artist can do. I am truly, truly skilled in many forms of fighting. After I get a victory Saturday night, I will most certainly look to compete in both sports."

McGregor even joked about conquering both MMA and boxing, then creating his own hybrid of the two as a new sport.