British boxer Dereck Chisora has slapped WBC heavyweight champion Vitali Klitschko at the weigh-in for their world title fight on Saturday.
Chisora's trainer Don Charles said his fighter's actions in Munich 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. I need to speak to [promoter] Frank Warren as to what happens next."
Asked whether it was pre-meditated, Charles added: "I'm not Dereck Chisora. Like I said, it's unacceptable."
BBC 5 live boxing reporter Mike Costello, who was at the weigh-in, said the 28-year-old's antics were "disgraceful".
"Somehow, Klitschko refrained from hitting back," said Costello. "He looked shocked. It has never happened to him before."
Chisora is a big underdog going into the fight but 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.