UFC middleweight champion Robert Whittaker was slated to face Luke Rockhold in the main event at UFC 221, but it appears that an injury has forced "Bobby Knuckles" to the sidelines. 

Whittaker's injury was first reported by ESPN's Brett Okamoto on Friday with additional news that Yoel Romero will be stepping up to face Rockhold instead. The new main event at UFC 221 will still have championship gold resting in the balance as Rockhold vs. Romero will fight for an interim strap with the winner facing Whittaker in a unification bout later in 2018.

Breaking on ESPN: Robert Whittaker has pulled out of UFC 221 next month due to injury. Luke Rockhold vs. Yoel Romero for interim title will headline, per UFC. Whittaker will face winner. https://t.co/fhl4dCXUHR

— Brett Okamoto (@bokamotoESPN) January 13, 2018

The middleweight division had recently rid itself of interim chaos as Whittaker became the undisputed champion when Georges St-Pierre officially vacated the title following his victory over Michael Bisping at UFC 217. In the weeks that followed St-Pierre's triumphant return to the cage after more than four years away from the Octagon, "GSP" announced a medical condition would prevent him from competing for a lengthy stretch.

St-Pierre's move allowed Whittaker to exchange his interim title for the undisputed crown, and news of the fight with Rockhold signaled a return to business for a division that had been slowed by chaos for the past year. Rockhold and Romero competing for an interim strap further signals to said return, but Whittaker suffering an injury is unfortunate nonetheless.

Finally, Friday's news confirms two additional points in we still cannot have nice things in MMA, and the UFC's love for interim belts continues to roll strong.