Light heavyweight champion Jon Jones will defend his title Sept. 27 at UFC 178, but he won't do so against Alexander Gustafsson.

The top contender suffered a knee injury that forced him to withdraw. Stepping in to fill the void is No. 2 contender Daniel Cormier; UFC officials revealed the news Wednesday night.

Cormier was slated to undergo surgery this month for lateral collateral ligament and antreior cruciate ligament injuries that an MRI revealed shortly after his May 24 victory over Dan Henderson. Cormier, however, decided to postpone the procedure.

The former No. 1-ranked heavyweight contender dropped to 205 pound rather than fight close friend and training partner UFC champion Cain Velasquez. Cormier improved to 15-0 at UFC 173 with a third-round rear-naked choke of Henderson. During the in-cage postfight interview, he put Jones on notice.

"No matter where you go boy, I'm coming," Cormier said. "You better hurry because I'm getting better." "I know nobody can wrestle me. It doesn't matter. If I decide to take Jon Jones down 100 times, I'll take him down 100 times. This is my octagon."

Jones and Gustafsson were tentatively slated to meet in a rematch on Aug. 30. Jones won the first showdown by a closely contested unanimous decision [Sept. 21, 2013, at UFC 165], but he was slow to sign the rematch agreement.

The more it seemed that the fight might fall through, the more impatient Cormier became. During an interview with SportsWorldNews.com, Cormier said he would step in to face Gustafsson, if the bout would be for the interim 205-pound title.

Shortly thereafter, UFC president Dana White revealed that Jones preferred to face Cormier.

"He doesn't want to fight Gustafsson," White said. "[UFC co-owner] Lorenzo [Fertitta] and I have a meeting with Jones ... to get him to sign the bout agreement and he's asking to fight Cormier instead."

Jones, who eventually signed the rematch agreement, is regarded as the pound-for-pound best mixed martial artist. In his most recent outing on April 26 at UFC 172, Jones [20-1] dominated hard-hitting Glover Teixeira en route to a unanimous decision.