BERLIN -- A German hospital on Wednesday discharged a member of the Russian protest group Pussy Riot after he made significant progress in his recovery from a suspected poisoning.

The Charite hospital said Pyotr Verzilov is no longer showing the symptoms of disorientation that he had when he arrived in mid-September after his initial treatment in Moscow. It said there's still an issue with the reaction of his pupils, but doctors are confident that will disappear.

Verzilov and other members of Pussy Riot served 15-day jail sentences for disrupting the World Cup final in Moscow in July to protest Russian police brutality.

German doctors treating Verzilov have said reports that he was poisoned are "highly plausible," but stressed they can't say how this might have occurred or who was responsible.

Verzilov fell ill on Sept. 11 after attending a friend's court hearing in the Russian capital, and was admitted to a Moscow hospital that evening with symptoms that included disorientation and widened pupils. Russian doctors suspected possible poisoning and treated him accordingly, emptying his stomach and performing a dialysis, German doctors say.

The Charite's Dr. Kai-Uwe Eckardt said the diagnosis of an anticholinergic syndrome hasn't changed, and "an intake or absorption of an exogenous substance as the cause of this syndrome still appears to be the most plausible explanation for his acute illness on Sept. 11."

Tests during his stay at the hospital have produced no indications of another cause, Eckardt added.

Charite's chairman, Dr. Karl Max Einhaeupl, added that tests so far haven't produced any clear indication of a specific substance that might have caused his illness. He said the Berlin hospital remains in contact with its Moscow counterparts to get more information on Verzilov's initial treatment.