A performance artist and member of the Russian protest group Pussy Riot has been hospitalized with a serious condition after attending a court hearing for another member of the group on Tuesday.

Pyotr Verzilov, who was among the protestors who invaded the soccer pitch at the World Cup Final in Russia, is thought to have been poisoned.

Verzilov was in court for a hearing of Veronika Nikulshina on September 11 before he was taken ill. Nikulshina has spoken to the Russian news website Meduza, saying Verzilov fell ill shortly after the hearing, and within a few hours began to lose sight, speech and mobility. Between 8pm and 10pm that evening, “[He] became worse in geometric progression,” Nikulshina said. “First sight, then the ability to talk, then the ability to walk right.”

He was taken to the toxicology department of the Bakhrushin City Clinical Hospital in Sokolniki. Relatives told the Russian website that his mother was not permitted to see her son when she visited yesterday, September 12, and was not given any information about his condition or suspected diagnosis.

The official Pussy Riot twitter account tweeted about the incident, writing “Our friend, brother, comrade Petr Verzilov is in [sic]reanimation. His life is in danger. We think that he was poisoned.”

Both Verzilov and Nikulshina were taken into police custody earlier this week by “anti-extremism agents,” Verzilov at his home and Nikulshina while driving with a friend. The hearing was over Nikulshina’s alleged refusal to submit to a “terrorist check” of her car, although the group believes it the arrests were a retaliation from the Russian government over the World Cup stunt.

Member of the Pussy Riot punk group Pyotr Verzilov gestures as he walks with police during a court hearing at a courthouse in Moscow, on July 31, 2018. Photo by Vasily Maximov/AFP/Getty Images.

Verzilov is married to Nadezhda Tolokonnikova, one of the group members who was jailed for two years in 2012 following a performance art piece at a cathedral in Moscow. Tolokonnikova tweeted “My brother Pyotr in intensive care may have been poisoned. In the toxicology department in a very serious condition.” Another member, Maria Alyokhina, also tweeted about the incident.

Verzilov is a Canadian citizen and the publisher of the Mediazona publication created by Tolokonnikova and Alyokhina. He was jailed for 15 days earlier this year along with three female members of Pussy Riot after their pitch invasion during the World Cup in Moscow, an action meant to draw attention to human rights abuses in Russia. He was part of the controversial performance art group Voina (War) with Tolokonnikova, until they split from it 2009, and has been a de facto spokesperson for Pussy Riot since 2012.