UFC light heavyweight champion Daniel Cormier (16-1 MMA, 5-1 UFC) knows his first title defense will come against Swedish contender Alexander Gustafsson (16-3 MMA, 8-3 UFC), but it won’t happen when the two originally planned.

MMAjunkie today learned from a person close to the fight who spoke on the condition of anonymity because he is not authorized to publicly discuss such matters that a lingering Cormier knee injury will force a delay on the fight, which UFC officials tentatively penciled in for September’s UFC 191 event in Las Vegas.

A UFC official subsequently confirmed the current state of the matchup but classified it only as a “slight delay” and indicated Cormier could be ready to fight as soon as October.

The exact nature of the injury wasn’t immediately known.

UFC President Dana White in June first mentioned the UFC’s plans for the fight, though an exact date for the contest was never announced.

Gustafsson, No. 4 in the latest USA TODAY Sports/MMAjunkie MMA light heavyweight rankings, last appeared in the octagon at UFC on FOX 14 in January when he suffered a first-round knockout loss to Anthony Johnson. The bout was a No. 1 contender matchup, and “Rumble” went on to face Cormier for the vacant UFC light heavyweight title at May’s UFC 187 event.

UFC 191 takes place Sept. 5 at Las Vegas’ MGM Grand Garden Arena. The evening’s main card airs on pay-per-view.

For more on UFC 191, check out the UFC Rumors section of the site.