Brett Yormark, the longtime face of the rebranding efforts at NYCB Live’s Nassau Coliseum, has left the company that renovated and operates the Uniondale arena.

Yormark’s last day overseeing Coliseum business and programming operations was Sept. 18, according to Maureen Hanlon, president of Mikhail Prokhorov’s Onexim Sports and Entertainment, which holds the lease on the Coliseum, which Nassau County owns.

Yormark said in an interview he left Onexim because his responsibilities diminished after e-commerce billionaire Joseph Tsai’s purchase of the Brooklyn Nets and Barclays Center from Prokhorov, a Russian billionaire.

That sale did not include the lease to the Coliseum. That means Onexim will be responsible for booking Coliseum programming such as concerts, sporting events and family shows, Hanlon said.

Yormark, 52, said he enjoyed booking events for the Coliseum, but that he had wider responsibilities. Before the sale, Yormark was chief executive of BSE Global, responsible for the Nets, Barclays Center and the Coliseum.

Had Yormark remained with Onexim after the transaction, he only would have been in charge of Coliseum. Tsai last week hired former Turner president David Levy to replace Yormark as CEO of the Nets and Barclays.

“I’m still bullish on the Coliseum, Onexim ownership is still bullish on the Coliseum,” Yormark said Tuesday. “I had to look at the bigger picture and I believe I’ve got another chapter in my career, maybe two. I've got to move on.”

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Hanlon said Coliseum operations won’t change significantly because she has been involved with the arena operations since the start of the $180-million renovation project several years ago.

“The commitment to it remains the same,” Hanlon said of Onexim.

Yormark also served as a spokesman in dealings with the county and at public meetings for Onexim's proposal with Uniondale-based RXR Realty for a $1.5 billion commercial and residential redevelopment of the 77 acres surrounding the Coliseum at the Nassau HUB.

Hanlon noted she was at those same meetings, and Yormark’s departure does nothing to change their plans at the Hub site. “We think it can bring the Coliseum to another level,” she said.

Nassau County Executive Laura Curran said she has been in contact with Coliseum executives since Yormark left last week.

“While we will miss Mr. Yormark’s personal commitment to the Hub, we are confident in the Coliseum management and the partnership forged with RXR,” Curran said in a statement.

“We are excited to see the Hub project move forward, transforming a sea of pavement into an innovative, vibrant community where future generations can live, work and play,” Curran said.

Onexim promoted Nick Vaerewyck this month to oversee all programming, marketing, sales and communications at the Coliseum in Yormark’s absence.

“It was a group effort in the past, and it will continue to be that same effort from me in the future,” Vaerewyck said.

Yormark, who ran the Nets for 14 years, said he’s weighing opportunities in the sports industry.