Jan Blachowicz withdrew from the March 26 UFC Fight Night main event against Aleksandar Rakic, he announced on Twitter.
Blachowicz said he suffered an injury in his spine around the neck.
The UFC hopes to reschedule the bout - a sentiment that Blachowicz shares - and the March 26 card is expected to receive a new main event, sources told MMA reporter Ariel Helwani.
The fight was set to be Blachowicz's first match since losing the light heavyweight championship to Glover Teixeira by submission last October. The former champion was on an impressive five-bout win streak before falling to Teixeira, etching victories over Israel Adesanya and Dominick Reyes, among others.
Blachowicz has compiled a 28-9 record over his career, while Rakic owns a 14-2 mark.