Russian officials say the artistic director of the Bolshoi ballet will need at least one more operation after an attacker threw acid in his face and that it’s not yet clear if the sight in his right eye can be saved.

No arrests have been made in the Thursday night attack on Sergei Filin, which his colleagues say may have been retaliation for his selection of certain dancers for prized roles.

Filin underwent surgery on Friday.

Alexei Levchenko, a spokesman for Russia’s deputy prime minister, was quoted by the state news agency ITAR-Tass as saying Filin was in stable condition after the operation but that “the prospects for restoring his sight will be clearer in five to seven days.”

Filin might have another operation next week, Levchenko said.