Moscow ? A jailed Russian oil tycoon won a small victory Tuesday when a court in the Siberian town where he is imprisoned reportedly ruled that his transfer to solitary confinement earlier this year was unlawful.

Prison authorities, however, later announced that the tycoon, Mikhail Khodorkovsky, would be returned to an isolation cell out of concerns for his safety after he was slashed in the face while sleeping last week.

Khodorkovsky, 42, is the former chief of the Yukos oil company and was once Russia’s richest man.

He was convicted on charges including fraud and tax evasion after a trial seen as punishment for his political ambitions and part of a state drive for control of the crucial oil industry. Yukos has been dismantled, and its main production unit is now under state control.

He was sentenced to eight years in prison last May, and placed in an isolation cell for five days in January after he was found in possession of Justice Ministry documents on inmates’ rights.