The artistic director of the Bolshoi Ballet is being treated in hospital in Moscow for severe burns after a masked man threw acid in his face.
The attack happened late on Thursday as Sergei Filin, an award-winning ballet star, was walking home in central Moscow.
Doctors are trying to save his eyesight and Interfax news agency said he will be sent to a clinic abroad.
Mr Filin took as artistic director at the Bolshoi in March 2011.
Tensions at the Bolshoi over the artistic programme have been widely reported in Russian media and the company said Mr Filin, 42, had been receiving threats for months.
A BBC correspondent said 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.
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.