Shakur Stevenson says he has secured a release from Zuffa Boxing without fighting for the promotion.
Multiple-weight world champion Stevenson, 29, was one of several high-profile signings for the Saudi Arabian-backed boxing promotion headed by UFC owners TKO and Dana White.
He was in talks to fight WBO welterweight champion Devin Haney but those discussions appear to have broken down – with Stevenson saying he was now a "free agent".
"I requested to be released from Zuffa Boxing," Stevenson said on his Youtube channel.
"Now, over the weekend, my request has been granted."
Zuffa Boxing has not comment on Stevenson's suggested exit from the promotion.
White has vowed to take over boxing and his most eye-catching signing was that of Conor Benn, poaching the Briton from Matchroom and Eddie Hearn.
Benn has now had two fights with Zuffa, the second being last month's quick knockout defeat by world champion Ryan Garcia.
Stevenson's last outing was an impressive win against American rival Teofimo Lopez, when he became a four-weight world champion.
The New Jersey native was keen to be become a five-weight world champion by fighting Haney, but Stevenson says he has been left frustrated by being on the sidelines since signing with Zuffa in July.
"I've been in camp for like eight weeks, preparing for fights that I was told was going to happen and have not happened," Stevenson said.
"It is what it is. This is the business of boxing. I'm not mad at anyone, I'm not pointing fingers.
"I am taking my career in my own hands and starting my own promotional company and I'm willing to work with other promoters and anybody else that's willing to be as serious about my career as I am," he added.
Stevenson says he now plans to defend his WBO light-welterweight world title before moving up to welterweight in the coming years.