Mayweather CEO Responds to McGregor, 'Come Get 2nd Ass Whooping!'

If Conor McGregor is serious about a rematch with Floyd Mayweather, all he needs to do is call ... this according to Mayweather Promotions CEO, Leonard Ellerbe.

Ellerbe runs Floyd's boxing business and has had his hands in some of the biggest events in the company's history ... including the McGregor and Pacquiao fights.

So, now that Conor has publicly stated he wants a second crack at Floyd, we asked Leonard if Mayweather would be down.

"Conor McGregor knows he's always welcome to that ass whooping," Ellerbe tells TMZ Sports.

"If Conor wants some of that smoke again, he knows what he's gotta do."

Long story short ... Ellerbe says Conor just needs to pick up the phone and call and they can get the ball rolling.

Even though Ellerbe says he hasn't spoken to Floyd about the fight, he's CERTAIN the 50-0 legend would dust off the gloves for another 9-figure payday.

But, Ellerbe says Floyd doesn't NEED the money ... noting he's heavily invested in real estate -- he owns several buildings in Times Square -- and he's set for life.