But for the first time, the man they call Money admitted the 28-year-old Irishman stood a chance against him in the boxing ring—because of their ages.
"I've been off for a couple years and I'm 40 years old now," Mayweather told TMZ at an event in Los Angeles on Tuesday. "So, I'm a lot older and he's still in his twenties and I'm in my forties now. So that could play a major key, we don't know. And he's a heavy hitter. … Does he have a good chance of upsetting Floyd Mayweather? I can't say, but anything can happen in the sport of boxing."
"Every time he goes out there and defeats fighters, he's standing up," he said. "He's in a boxing position and he's beating fighters."
Still, the undefeated 40-year-old took a shot at McGregor, by implying that the UFC bad boy isn't even the biggest star in his sport, thanks to Mayweather himself.
"Conor McGregor is the second-biggest name in MMA."