Just hours after Kamaru Usman's welterweight title defense Saturday night, Conor McGregor sent out a tweet. It read: "145. 155. 170."

McGregor has already held UFC titles at featherweight and lightweight -- or 145 pounds and 155 pounds. The 170 represents the pound limit for welterweight. It sure seemed like McGregor was calling for a title shot against Usman with that tweet. And that's how Usman took it, too. The champion doesn't think McGregor would fare too well as challenger at that weight class.

"He must want to die," Usman told TMZ on Monday. "This is not '45, '55. You saw what Khabib [Nurmagomedov] did to him. Oh my God. It wouldn't be fair if I fought Conor. Much respect to Conor for what he's done for the sport and transcended it. But nah. This ain't what you want. Just sit down, little man. Sit down. Learn to walk before you can run. Because I would hurt that guy."

Usman finished heated rival Colby Covington by TKO in the fifth round Saturday in the main event of UFC 245 in Las Vegas. It was a close fight until the finish, but Usman did the majority of the damage, breaking Covington's jaw in the third round.

The victory was a star-making performance for Usman. Covington was the agitator leading in, talking heaps of trash. It is viewed now like Usman shut him up, and he is getting major props for that in the mainstream.

As for possible next opponents, Usman (16-1) said "eh" in reference to Jorge Masvidal. The foe he would want most is currently retired: the best welterweight of all time, Georges St-Pierre.

"If I had to choose, of course I want Georges," Usman said. "I want GSP. One more win and I tie him for the most consecutive wins. How sweet would that be to actually get that win off of him?"

GSP won 12 straight UFC welterweight fights between 2007 and 2013. The 32-year-old Usman has won 11 in a row from 2015 to the present. But St-Pierre has not fought a comeback fight after a four-year layoff in 2017 when he won the UFC middleweight title from Michael Bisping.

GSP, 38, continues to train in MMA at Tristar Gym in Montreal, but he has formally retired and removed himself from the UFC's USADA-led drug-testing pool. In order to fight again, he'd have to re-enter the pool and be tested for six months prior to competing. St-Pierre has expressed interest in returning to fight lightweight champion Nurmagomedov, but the UFC has not been in favor of the idea.

Usman, though, wants to throw his hat in the ring if there's any possibility.

"I think it's a big, big, big fight," Usman said. "All due respect to Georges, but I think I finish him."