T.J. Dillashaw said last week he believed his scheduled Saturday opponent and former bantamweight champion Renan Barao had outgrown the division.
Friday, Dillashaw's opinion struck sooner rather than later, depriving the new champion of an opportunity to affirm his May upset of Barao with a repeat victory.
Barao fell ill while cutting weight and has been replaced in the Ultimate Fighting Championship main event at Sleep Train Arena in Sacramento.
Scheduled undercard fighter Joe Soto (15-2) will step in for Barao, the UFC announced, and the jumbled fight card will remain on pay-per-view, a company spokesman said.
Barao "was feeling poorly … in the process of his weight cut," the UFC spokesman said. A "decision was made to pull him from [the] fight based on his health and safety."
Soto has won six consecutive mixed martial arts fights, but he's a sharp drop in talent from Barao, who hadn't lost in nine years before meeting Dillashaw in May.
Soto just signed with the UFC this month.
Barao (32-2) was an 8-1 favorite in Nevada sports books in May before Dillashaw surprised him with his hand and foot speed, knocking down the Brazilian with a crushing right-handed punch to the jaw in the first round, and proceeding to finish him in the fifth round with a head kick and punches.
Barao had been anointed by UFC President Dana White as the organization's top pound-for-pound fighter before the bout and later said he remained wobbly through the fight due to the knockdown punch in the first.
Soto, from Porterville, Calif., was due to fight Anthony Birchak on Saturday's undercard. The Sacramento card already suffered a hit when the co-main event 125-pound title fight between champion Demetrious Johnson and Chris Cariaso was shifted to Sept. 27 due to an injury to light-heavyweight champion Jon Jones.