London-born Dereck Chisora fanned the flames ahead of Saturday's WBC heavyweight title challenge by slapping reigning champion Vitali Klitschko at Friday's weigh-in in Munich.
The pair squared up for photographers after stepping off the scales, Chisora, wearing a Union Jack bandit scarf, butted heads with his opponent before slapping the Ukrainian. Klitschko however did not retaliate.
BBC Radio 5 Live boxing presenter Mike Costello witnessed the incident. "Chisora leant back and slapped Klitschko hard - very hard - with his right hand on the left-hand side of Klitschko's face," he said.
Promoter Frank Warren’s son, Francis, was on hand to represent his father’s company, and admitted that "We're all scratching our heads about it, to be honest,” reported BBC Sport.
"You always expect something from Dereck - he's a character - but it's usually something that winds people up or is a bit jovial.
He added: "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."
Even Don Charles, Chisora’s trainer, branded the slap as “unacceptable”.
Chisora is a rank outsider ahead of the weekend's fight but has vowed to cause a “massive upset" in Germany. He weighed in at 17 stone 3lbs - just a pound heavier than his lightest weight for a professional bout. Klitschko meanwhile came in at 17 stone 6lbs.
The fight will take place at the Olympia Halle in Bavaria.