UFC president Dana White says Brock Lesnar is retiring and will not be fighting Daniel Cormier.
Earlier this year it was reported that Lesnar and Cormier could be set for a heavyweight title showdown this summer.
But, when asked about Lesnar on ESPN on Tuesday, White said: "He told me he's done.
WWE superstar Lesnar, 41, has not fought in the Octagon since defeating Mark Hunt at UFC 200 in July 2016 - a victory which was later changed to a no-contest after Lesnar failed a drug test.
Lesnar recently lost his WWE Universal title, when he was defeated by Seth Rollins at Wrestlemania.
In the absence of Lesnar, the UFC are close to agreeing a heavyweight showdown between Comier and former champion Stipe Miocic.
Miocic told ESPN: "I'm ready.
"And I'm going to take back what's mine."