Tuesday, TMZ published an interview with Floyd Mayweather, in which the boxing champion delivered his prediction for Conor McGregor's upcoming MMA fight with Khabib Nurmagomedov on Oct. 6. Mayweather seemed to be pulling for McGregor, his boxing foe in August 2017. 

"Conor McGregor, he's a tough competitor," Mayweather said. "Like I said before, Conor McGregor's not gonna back down from anyone, he's not scared, he's a warrior."

Floyd also invited Conor to come to Las Vegas and train at Mayweather's home gym. But the Irish UFC star is having none of the love. He tweeted that "there is no peace" in their relationship.

With the "step up or step down" challenge, McGregor appeared to call on Mayweather to meet him in the Octagon. They had fought on Mayweather's home turf; now, McGregor seems to be implying, it's time to throw down on McGregor's. His tweet later Tuesday seemed to imply the same thing—his last fight marked an "outside trip."

Mayweather, who defeated McGregor by TKO in the 10th round of their boxing match, quickly clapped back at Conor.

The UFC announced Aug. 3 that McGregor would make his highly anticipated MMA return at UFC 229, where he'll face emerging rival Khabib, who now holds the UFC lightweight championship. Conor hasn't fought in the Octagon since UFC 205 in November 2016.