LONDON (AP) -- One of the ballet world's brightest but most volatile stars has vanished, again.
Sergei Polunin had been due to star in a dance piece based on Billy Hayes' Turkish prison memoir "Midnight Express" opening next week in London.
But director Peter Schaufuss said the 23-year-old dancer did not show up for rehearsals on Wednesday.
Schaufuss told the BBC he was "hugely disappointed" the young star had left.
"I'm really, really worried about him," the director said. "Artists have good and bad days -- that goes with the territory -- but rehearsals were going well."
The dance company said Polunin's mentor, Igor Zelensky, had also left the production.
Polunin's whereabouts could not immediately be determined Friday. But friend Anthony Lammin -- who co-owns a London tattoo parlor with the dancer -- told the Evening Standard newspaper that Polunin was OK.
"I don't know why he left the show," Lammin said. "We have been texting each other during the last few days. He's fine and is doing well."
Ukraine-born Polunin became the youngest-ever male principal dancer at Britain's Royal Ballet when he was 19, but walked out of the company last year, saying he was giving up dance.
He later said he had quit because he could no longer handle the stress of a dance career.
Polunin, who moved to Britain aged 13, had spoken in a 2011 interview about the pressure he felt to succeed.
"I would have liked to behave badly, to play football. I loved sport," he told The Guardian. "But all my family were working for me to succeed. ... There was no chance of me failing."
Polunin later returned to performing under Zelensky at Moscow's Stanislavsky Ballet and has made guest appearances with the Royal Ballet.
When his role in "Midnight Express" was announced late last year, Polunin said it was "exactly the kind of work I want to be making, and I'm thrilled to be a part of it."
The Peter Schaufuss ballet company said Danish understudy Johan Christensen would take over the main role in "Midnight Express," which opens Tuesday.
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