Daniel Cormier will fight champion Jon Jones for the light heavyweight title at UFC 178, replacing injured Alexander Gustafsson.
The UFC announced the new match Wednesday night for Jones, the promotion's pound-for-pound star.
UFC 178 is Sept. 27 at the MGM Grand Garden in Las Vegas.
Cormier (15-0) is a former U.S. Olympic wrestler who excelled as a heavyweight before moving down to 205 pounds this year. He was scheduled for knee surgery in July, but put it off.
Cormier already has a vocal public rivalry with Jones (20-1). Both fighters traded insults on social media immediately after the bout was announced.
Gustafsson (16-2) injured his knee in training, the UFC says. He was scheduled to meet Jones in a rematch of their memorable 2013 bout in Toronto.