Story highlights Sergei Filin was attacked as he approached his home in Moscow on Thursday night

The unidentified assailant threw concentrated acid in his face, causing severe burns

Filin had suffered intimidation, including threatening phone calls, state media say

Doctors are fighting to save the sight of the artistic director of Russia's illustrious Bolshoi Ballet after a masked assailant threw acid in his face on a Moscow street, state media reported.

Sergei Filin, 43, was approaching his home around midnight Thursday when the unidentified attacker flung the concentrated acid at him, causing severe burns to his face, the state-run news agency RIA Novosti reported Friday.

It could take Filin at least six months to recover from the third-degree burns to his face and eyes, RIA Novosti cited Yekaterina Novikova, a Bolshoi spokeswoman, as saying.

Filin took up the key role at the world-renowned ballet company in 2011, after three years directing Moscow's Stanislavsky and Nemirovich-Danchenko Music Theater.

There was "fierce rivalry" for the Bolshoi position at the time, according to RIA Novosti.

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The agency reported that Filin had suffered months of intimidation, including threatening phone calls and the slashing of his car tires. Shortly before the acid attack, somebody attempted to hack his Facebook page, it said.

"We don't know who would benefit from this," Novikova told RIA Novosti. "The police should investigate."