Conor McGregor has been issued a boxing licence and is said to be pursuing a "high-level opponent".
The Irish fighter and one of UFC's highest-profile and biggest-earning figures has previously been linked to a fight with the now-retired boxer Floyd Mayweather.
After McGregor's most recent victory in November against Eddie Alvarez to become the world's first simultaneous two-weight champion, he demanded a stake of the UFC company's ownership.
That came after he said he wanted $100 million (£80 million) to box the undefeated Mayweather in a glamorous - but perhaps uncompetitive - match-up earlier this year.
"He got a licence and a federal ID," California State Athletic Commission executive officer Andy Foster told MMAFighting.com. "He's a California boxer now.
"I'd love to see him fight in California. It just needs to be the right opponent. Certainly a high-level opponent. We're happy to license him."
The development may be interpreted as McGregor - who has vacated his two titles - attempting to force the UFC to submit to his demands, but it also follows his trainer John Kavanagh saying earlier this week that he would "put on few quid on (a Mayweather fight) next year".
"I'm not breaking any news saying that there's conversations going back and forth for the last year or so," he added.
"Is it getting any close? I don't know, but it certainly wouldn't surprise me that it's going to happen."
Mayweather, however, had previously said of the prospect of them fighting: "I'm an elephant. Elephants don't beef with ants."
Leonard Ellerbe of Mayweather Promotions had also told ESPN on Wednesday: "It's all a game, a calculated effort to gain more fans. Conor McGregor can say anything he wants to, but he has a boss and his name is (UFC president) Dana White."
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