Heavyweights Derrick Lewis and Sergey Spivak were set to battle at UFC Vegas 65 on Saturday at the Apex in Las Vegas.
Instead, cageside announcer Brendan Fitzgerald interrupted the prelims to announce that the main event was canceled due to a "non-COVID, non-weight cutting illness on the Derrick Lewis side."
The light heavyweight bout between Kennedy Nzechukwu and Ion Cutelaba was upgraded from co-main event to the main event and will remain three rounds, according to the broadcast.
Lewis (26-10 MMA, 17-8 UFC) is the UFC's all-time KO leader.