Everyone has been clamoring for the Mayweather-McGregor fight ever since Mayweather started spreading the rumors himself. McGregor seems just as excited. However, there’s one person who thinks the Irish MMA fighter should tread lightly. That is Joe Rogan, a veteran UFC commentator.

Talking to Rolling Stone, Rogan said of the rumored fight, “And it wouldn’t be a good fight for Conor. I can’t imagine a world where Floyd Mayweather doesn’t box as good as Conor.”

Joe Rogan was quick to point out that it is going to be harder for a boxer to switch to MMA rather than the other way around. For a boxer to switch, there is a greater learning curve to overcome, especially in grappling. With the grappling and other martial arts that a boxer has to learn in a short span of time, a boxer will do good to just stay in his boxing ring rather than enter an MMA cage.

Rogan even lists MMA fighters who can enter the boxing world and end up victorious. From Uriah Hall’s fast punches to Anderson Silva, Joe Rogan believes these MMA fighters know enough of boxing to be efficient fighters.

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Although Rogan has already said the Boxing vs MMA fight won’t bring any good to McGregor, he is confident that McGregor will be able to teach Mayweather not to mess with MMA fighters in the future. Tagged as the “Billion Dollar Fight” by The Independent, McGregor and Mayweather may be up for a huge payday if it happens.

“But what do I think would happen if Roy Jones Jr. fought Conor in an MMA match? Conor would fuck him up, 100 percent,” Joe Rogan predicts.

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He compared the upcoming “rumored” fight against a one-time match between Olympian Ray Mercer and MMA fighter Tim Sylvia. Rogan points out that even though Mercer knocked Sylvia out cold on the MMA cage floor, Mayweather isn’t half of the puncher that Mercer is.

“I mean, maybe the UFC co-promotes it with Floyd Mayweather and Conor goes in there and gets lit up, and then says, ‘Hey, I realize this is not my sport, I gotta go back to MMA,’ then that’s possible too.” At least, that is what Rogan thinks McGregor will say after he’s had his taste of boxing—a wake up call of sorts to tell him why he is in MMA in the first place.