The artistic director of Russia's Bolshoi Theatre, Sergei Filin, is being treated in a Moscow hospital for severe burns to his face after a masked man threw acid in his face, police say.
The attack happened late on Thursday as Mr Filin, an award-winning ballet star, was walking home in central Moscow.
Doctors are now fighting to save his eyesight and Interfax news agency says he will be sent to a clinic abroad.
A Bolshoi spokesman said Mr Filin, 42, had suffered months of threats.
The BBC's Steve Rosenberg in Moscow says it is suspected that he was the victim of infighting and rows between different groups of dancers at the Bolshoi.
According to the Bolshoi statement, the assailant shouted to Mr Filin as he was approaching the entrance to his apartment block, then threw acid in Mr Filin's face.
Mr Filin then got help from a warden keeping watch over nearby cars.
The theatre's executive director, Anatoly Iksanov, told Russian television that Mr Filin was "uncompromising" in his management style.
"If he thought a performer was unready to play a certain role, or incapable of it, he would not let the performer do it," he said.
Tensions at the Bolshoi over its artistic programme have been widely reported in Russian media.
In 2011 two ballet stars - Natalia Osipova and Ivan Vasiliev - resigned in protest at the Bolshoi's new repertoire.
At the time of Mr Filin's appointment the head of the Bolshoi's ballet troupe, Gennady Yanin, resigned after erotic photographs purporting to be him were posted on a website.
Another celebrated performer, Nikolai Tsiskaridze, sharply criticised Mr Filin in early 2012.