American Tony Ferguson will step up to take on compatriot Nate Diaz in the main event at UFC 279, after Swedish fighter Khamzat Chimaev missed the weight for the welterweight showdown by a whopping 7.5 pounds (3.4kg).
Chimaev, 28, tipped the scales at 178.5 pounds (81kg), with his team saying a "medical issue" prevented him from cutting weight effectively.
Fighting in the last bout of his UFC contract, the 37-year-old Diaz weighed in at 171 pounds (78kg), as did Ferguson, who was due to meet Chinese fighter Li Jingliang in the co-main event.
With Diaz and Ferguson now to clash, Chimaev will take on Kevin Holland at a 180-pound (82kg) catchweight, while Li will take on another Californian in Daniel Rodriguez.
There was controversy in the build-up to the event, as the news conference was abandoned after trouble backstage, with Chimaev and Holland getting into an altercation, after by a row between Chimaev and the Diaz entourage.
With both sides of that scuffle well represented in the auditorium, UFC president Dana White closed down the news conference quickly, rather than risk an outbreak of violence.
"You don't have to be a rocket scientist to figure out where this whole press conference was headed, and there were so many people with all the camps that, once that started, that would have been bad," White said.
The Las Vegas Metropolitan Police greeted people arriving for the official weigh-ins at the UFC's Apex building.
Reuters