Steve McCarthy, who lost a fight to a shoe wielded by an opponent's mother, withdrew from the rematch today because of the flu.
"He is genuinely ill," said Jack Bishop, McCarthy's manager. "He's very sick."
McCarthy was to have fought Tony Wilson on Wednesday in a rematch of their light-heavyweight fight in September that was halted when Wilson's mother climbed into the ring and clobbered McCarthy with a high-heeled shoe.
McCarthy needed four stitches in his head and refused to continue the bout, which made headlines round the world. The referee awarded the fight to Wilson, and his decision was upheld by the British Boxing Board of Control.
Wilson's mother, Minna, apologized for her behavior and said she would never attend one of her son's fights again.
She said she was reacting to chants she regarded as racist from members of the crowd in Southampton.
The Wilsons, from Wolverhampton in the English midlands, are black. McCarthy, from Southampton, is white.