British boxer Dereck Chisora slapped heavyweight champion Vitali Klitschko at the weigh-in for their world title fight on Saturday.
Klitschko did not retaliate as the two men were pulled apart but vowed to take his revenge inside the ring in Munich.
"He hit me not like a boxer but like a woman, with an open hand," said the World Boxing Council (WBC) champion.
"If he wants to fight properly, he must do that with his fists. I'll be hitting him back tomorrow, in the ring."
Chisora, 28, is a big underdog going into the fight after suffering two high-profile losses in his last three fights.
Ukrainian Klitschko, 40, added: "He's not all there. Dereck is full of nervousness and I feel he is afraid, otherwise he would not have jumped back like he did."
Chisora's trainer Don Charles said his fighter's actions were "totally unacceptable".
"I'm speechless," he said. "I'm with him 16 hours of every day and I didn't see that coming. It's totally unacceptable."
Jose Sulaiman, president of the WBC, described the slap as "unacceptable" and suggested that Chisora could face a heavy fine.
He told BoxingScene.com: "This is definitely a lack of respect for the sport and completely unacceptable.
"It was a cheap shot and my message is that there is a fine so he'll [Chisora] feel it.
"He's no gentleman at all and he's failed in what we expect from boxers.
"He wanted Vitali to lose control but Vitali will make him pay for this in the ring, definitely."
BBC 5 live boxing reporter Mike Costello, who was at the weigh-in, said the Chisora's antics were "disgraceful".
"Somehow, Klitschko refrained from hitting back," said Costello. "He looked shocked. It has never happened to him before."
Chisora insisted on Thursday he would take Klitschko's title.
"I will end the Klitschko reign and cause a massive upset," said the Londoner. "It is the end for Vitali, I promise you."
Promoter Francis Warren, representing his father Frank's company, said: "We're all scratching our heads about it, to be honest.
"You always expect something from Dereck - he's a character - but it's usually something that winds people up or is a bit jovial.
"So for him to get physical and aggressive, unprovoked, is surprising. But I'm sure there's method to his madness and we'll find out if the madness has paid off tomorrow night."
Asked whether he expects sanctions against Chisora, Warren said: "That's up to the governing bodies to decide. If there are sanctions, then I suppose we will find out in the next couple of weeks.
"I'll sit down and have a chat with Dereck about it but at the moment we're focused on tomorrow night.
"Dereck is obviously a fiery character and that has got him to where he is. He can react like that to situations but he is a boxer, a fighter. Let's focus on the fight."
Chisora weighed in at 17st 3lbs, just a pound heavier than his lightest weight for a professional bout. Klitschko came in at 17st 6lbs.