Dereck Chisora threatened to shoot David Haye after the two were involved in a brawl at the news conference following Chisora's WBC heavyweight title loss to Vitali Klitschko.
Chisora accused Haye of "glassing him", before saying at least four times that he would shoot the former WBA heavyweight champion.
He added: "If David don't fight me, I am going to physically burn him."
Haye's manager, Adam Booth, also suffered cuts to his face in the post-fight melee.
Haye had been working for a television station and attended the news conference afterwards.
He was defeated by Wladimir Klitschko in Hamburg last summer and promptly retired from the sport.
However, he has since come out of retirement with the aim of setting up a fight with Wladimir's brother Vitali.
But during the conference, the Klitschkos's manager, Bernd Boente said: "With the bad experience we've had with British fighters we will now look for other countries.
"Contrary to David Haye, Dereck Chisora really went for it and really tried."
Haye, who was at the back of the room, replied: "You don't want to fight David Haye, no?"
Boente replied: "You had an offer, you didn't accept it, now you are out. You are out. Out, out, out. You cannot talk yourself back into the fight, you have no belts. Chisora showed heart, contrary to you. You showed your toe [Haye claimed he broke a toe before the fight]."
Chisora and his promoter Frank Warren then appeared to goad Haye into an all-British fight, with Chisora repeatedly saying "How's your toe?"
Haye hit back that Chisora was a loser, prompting Chisora to leave the stage and confront Haye, sparking the brawl.
At one point Haye picked up and swung a tripod and Booth, who was trying to break things up, was left with a wounded face.
After watching the unexpected drama unfold, Wladimir Klitschko told the BBC: "I'm totally disappointed, it went a little too far, the sport of boxing shouldn't be like that.
"Bloody faces in the press conference... fighting in the ring, not out. I'm really surprised."
It completes an ugly week for Chisora, who had part of his fight purse withheld by the World Boxing Council for slapping Vitali Klitschko in the pre-fight weigh-in on Friday afternoon.
Once in the ring, Chisora appeared to spit water in the direction of Wladimir Klitschko's face moments before the fight began. At the end of the contest, he went head-to-head with Vitali as the Ukrainian was awarded the belt he successfully defended.