Ronaldo "Jacare" Souza, who was due to oppose Uriah Hall in a middleweight bout, was scratched from the card after his test result was received.
However, the other 11 fights on the UFC 249 card will continue as scheduled at VyStar Veterans Memorial Arena in Jacksonville, Fla.
The UFC announced in a press release that two of Souze's cornermen tested positive for COVID-19, too.
"UFC's medical team examined Souza and his two cornermen and found them to be currently asymptomatic ...," the statement read, in part. "As per UFC's health and safety protocols, all three men have left the host hotel and will be self-isolating off premises, where UFC's medical team will monitor their conditions remotely and will provide assistance with any necessary treatment.
"From their arrival earlier in the week until their departure today, Souza and his cornermen followed UFC health and safety protocols, including practicing social distancing, wearing personnel protective equipment, and self-isolating whenever possible.
"There have been no other positive COVID-19 tests reported from the remaining athletes participating in UFC 249."
According to ESPN, Souza, a 40-year-old Brazilian, arrived in Jacksonville on Wednesday and told UFC officials that a member of his family previously tested positive for COVID-19. Although Souza had no symptoms, he was given a COVID-19 test and sent into quarantine.
The positive test result came back Friday, but ESPN reported that Florida state athletic officials are comfortable with UFC 249 moving forward because proper quarantine protocols were followed.
Souza (26-8) has lost four of his past six fights, including his last two. He most recently was in action last November, when he dropped a split decision to Poland's Jan Blachowicz in Sao Paulo.
Hall (15-9) is a 35-year-old Jamaica native who fights out of New York. He won his most recent fight, earning a split decision over Brazil's Antonio Carlos Jr. last September in Vancouver, British Columbia.
In the UFC 249 main event, Tony Ferguson (26-3) and Justin Gaethje (21-2) will battle for the organization's interim lightweight title.