Floyd Mayweather says a money-spinning bout with UFC champion Khabib Nurmagomedov "is happening".
But Mayweather says any fight with the mixed martial arts great would have to take place in the boxing ring.
After defeating McGregor himself at UFC 229 earlier this month to also stay unbeaten, Nurmagomedov said he now wanted to face Mayweather.
Speaking to TMZ, Mayweather said: "Oh — we fighting. I'm my own boss. So, I can't say what's going on, on Khabib's end. But, on my end, we can make it happen."
However, as with McGregor, Mayweather expects the fight to be in the ring rather than the Octagon.
"I'm Floyd Mayweather," he said. "I'm the A-side, you call me out, you come into my world.
"I don't know no other fighter that has done the numbers I have done. I don't know any fighters that have made the money I have made.
"So, he called me out — come into my world, make it happen.
"I see in an interview, he said when he hit Conor McGregor, he knocked Conor McGregor down.
"He said I didn't knock Conor McGregor down. OK, Khabib. You got my leftovers. Whoop-de-do."
Mayweather thinks he will make even more money fighting the Russian than he did when he took on McGregor.
"When I face Khabib, I'm getting a nine-figure payday," said Mayweather. "More than the McGregor fight. Probably $100 million more, guaranteed. It could be somewhere upwards of $110m to $200m, guaranteed."
But UFC heavyweight champion Daniel Cormier, who is a teammate of Nurmagomedov, declared the match-up a joke.
"Khabib better not try to box him. Khabib better not try to box Floyd Mayweather. What is he doing, man?' Cormier told ESPN.
"Unless he's just going to go do it for money, because he is going to get beat. I love Khabib man but he is going to get beat up by Floyd Mayweather. He's crazy. He is going to start wrestling. Khabib is going to start wrestling in the boxing ring. He's going to get beat so bad he is going to start wrestling."
A better fight, if Mayweather is serious about returning to the ring, would be the newly-crowned highest paid man in the sport Canelo Alvarez.
And the Mexican is keen on a rematch with Mayweather, who defeated him comfortably in 2013.
"He wants to continue hurting boxing by making fights that don't make sense ... and not giving boxing the credibility it deserves," Alvarez told TMZ Sports.
"If he wants to return, I ask him to look my way to give a great fight to the fans.
"Let's do the second fight. It's very important. We have something pending there, so let's make the second fight."