Conor McGregor mocked Justin Gaethje's performance against Khabib Nurmagomedov - before deleting his insult.
The Irishman was responding after Gaethje offered him a fight shortly after he was choked out by the now retired champion.
McGregor tweeted: "Dustin [Poirier] KO'd you, as well as your wrestling/grappling and overall fear of the central positions being truly embarrassing tonight, Justin."
The former two-weight champion quickly deleted the tweet.
Gaethje, who was choked out in the second round by Nurmagomedov, had called on McGregor to abandon his plan to fight Dustin Poirier in January and face him instead.
"With him retiring, I'm No. 1," he said. "Poirier and McGregor are going to fight [but] they haven’t made it official, so if McGregor wants to bounce out and get the belt, then I’m right here.
"If they want to give it to someone else, then so be it but I'll be ready. I’m ready to fight again; this is my job, this is my life. I love it so much."
Gaethje had ramped up his row with McGregor earlier in the week after a proposed fight between the pair earlier this year fell through.
"I've tweeted [McGregor] and called him a s*** father, human, and husband," he said. "That was in October and he fought Cowboy [Donald Cerrone] in January.
"He had every opportunity to fight me and he passed every time. The times he said he was going to fight, I never had a call from UFC or anybody to confirm whether that happened, so I don't know what was going on behind the scenes.
"But they never called me and he had many opportunities to fight me and he didn't. He chose Cowboy and I'd just knocked Cowboy out… that's a b**** move. And it will be a b**** move for the rest of his life."
McGregor had struck a conciliatory tone when he wished Nurmagomedov all the best in his retirement on Saturday night.
"Good performance Khabib. I will carry on. Respect and condolences on your father again also. To you and family. Yours sincerely, The McGregors," he wrote on Twitter.