Jake Paul has lashed out at Conor McGregor, accusing him of having "insecurity" and hinting that they will meet in a future boxing match.
McGregor makes his UFC comeback on Saturday night trying to avenge his recent defeat to Dustin Poirier.
But after going face to face with Poirier on Thursday night at a press conference, he was criticised by YouTuber-turned-boxer Paul who said: "You can tell Conor has lost 'it'.
"He no longer speaks from a place of authenticity and you can tell he's trying to convince himself of his own lies.
"He takes offence to everything now.
"He's bathing in his own insecurity.
"When we fight I will further expose him for the fraud he is."
Jake Paul also posted a picture taunting McGregor about his knockout loss to Poirier.
The social media superstar could emerge as a future option inside the boxing ring for McGregor.
The UFC's Irishman made a high-profile boxing debut in 2017 against Floyd Mayweather and was, until losing to Poirier, chasing a match against Manny Pacquiao.
Jake Paul, meanwhile, has won all three of his pro boxing matches via knockout and will next face former UFC champion Tyron Woodley on August 28.
Woodley is being trained by Mayweather, who recently went eight-rounds under an exhibition rule-set against Jake Paul's brother Logan.