The junior middleweight title fight between Ivana Habazin and Claressa Shields on Saturday has been called off after James Ali Bashir, the veteran trainer for Habazin, was struck by an unidentified person and knocked unconscious at a weigh-in Friday.
The assailant fled the scene, which took place at the Dort Federal Event Center in Shields' hometown of Flint, Michigan.
The fight between Habazin (20-3-0, 7 KOs) and Shields (9-0-0, 2 KOs) was supposed to take place Saturday night. It was one of three fights on the eight-bout card that was to be broadcast on Showtime (9 p.m. ET Saturday), which instead said it would televise only two.
The rest of the event will proceed as scheduled.
Video from Friday showed Bashir earlier involved in a verbal confrontation with an unidentified person during the weigh-in. It is unknown if the person involved is the same person who later attacked Bashir.
Bashir was knocked unconscious for approximately 20 minutes, witnesses told ESPN, before being taken out on a stretcher and brought to McLaren Medical Center. He was bleeding from his head after hitting the concrete floor.
Habazin went to the hospital with Bashir, who for years worked at the famed Kronk Gym in Detroit and was in the camp of longtime heavyweight champion Wladimir Klitschko.
Neither Shields nor Habazin took part in the weigh-in when it resumed Friday. Fighters on the undercard attended the delayed weigh-in, which was open to the public.
Dmitriy Salita, who promotes Shields, and Mark Taffet, Shields' manager, went to the hospital to see Bashir and Habazin.
The fights that will be broadcast by Showtime on Saturday night include a welterweight bout between Philadelphia's Jaron Ennis and Argentina's Demian Daniel Fernandez, and Jermaine Franklin taking on Pavel Sour in a heavyweight bout.
It was supposed to be Shields' first pro fight in her hometown. The two-time Olympic champion has won titles at the super middleweight level, and she unified the middleweight belts with a victory over previously unbeaten Christina Hammer in April. Shields took this fight at 154 pounds, trying to become a three-division champion.
"I had to lose a lot of weight for this fight, because I cleaned out the division at 160," Shields said earlier this week. "Every time I clean out the division, somebody else trying to tell me I'm not the greatest woman of all time, and I love when they say that because I want you to come show me I'm not the greatest woman of all time."
The Shields-Habazin fight was initially scheduled for Aug. 17, but it had to be postponed because of an injury to Shields.
ESPN's Steve Kim and The Associated Press contributed to this report.