The news was first reported by Ariel Helwani on Tuesday. It’s unclear what injury forced Smolka off the fight card.
O’Malley (13-1) rebounded from his first career loss in his last outing at UFC 260 in March, defeating Thomas Almeida by knockout in the third round. The win earned the 26-year old a performance of the night bonus.
Smolka (17-7) last competed in December 2020 picking up a TKO win over Jose Alberto Quinonez.
The fight was scheduled to be featured on the main card at T-Mobile Arena in Las Vegas. UFC 264 is headlined by the trilogy bout between former interim lightweight champion Dustin Poirier and form due-division UFC titleholder Conor McGregor.