Logan Paul has stepped in the ring with Floyd Mayweather, but he fared much different when in with a UFC fighter.

The YouTube star has mixed it with the best fighter of an era in Mayweather, but has yet to win a competitive bout.

Paul has lost to KSI in their rematch but is expected to return to the ring at some point this year, while his wrestling background could even point to an appearance in the UFC.

However, if this video is anything to go by, he wouldn't fare to well if he did step in the octagon, despite his positive working relationship with Dana White.

Paulo Costa's vicious KO of Logan Paul

The YouTube sensation shared a video online from a 2020 sparring session with professional MMA fighter Paulo Costa at the UFC performance institute in Las Vegas.

Paul did manage to land a few shots on his opponent, but his success is quickly ended with a swift right hook to the face from the Brazilian, which leaves the American internet sensation landing face down on the mat and seemingly out for the count.

The influencer then explained the KO shot in the video: "This morning we came here to the UFC performance institute. Apparently they want me to spar a guy by the name of Paulo Costa.

"He's not a human, he's a bear - he's 13 and 0 undefeated UFC fighter.

"I don't think he liked the way I looked at him at dinner last night or something - but it's a good thing I'm a professional boxer now who's 0 and 1, goddammit.

"They put the headgear on me, not him. That's how you know I'm f***ed."

Fans weren't sure whether to believe Logan Paul

Some viewers don't buy the story, though.

Looking at the knockout footage in slow motion, it seems that Costa landed the punch on Paul's left shoulder rather than in the head like the dramatic knockdown suggests.

Actually it's hard to clarify if Costa made any contact with the American at all, but the footage does show him left facedown on the canvas, so it could be set up as a stunt.

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Despite the one-sided nature of the sparring encounter, Costa's trainer praised Paul, revealing that he had actually impressed him during the grappling session.

He said: "You're going to do MMA for sure. You know how to fight."

Costa himself then added his own praise: "Ninety per cent of guys who go to train MMA have good technique, but not hard spirit, not big heart you know. You have both."