Open this photo in gallery (L-R) Nadezhda Tolokonnikova, activist and ex-wife of Pyotr Verzilov, Veronica Nikulshina, activist and Verzilov's current girlffriend, and Yelena Versilova, Pyotr's mother, speak to the media on Sept. 18, 2018 in Berlin, Germany. Sean Gallup/Getty Images

The medical team treating a Canadian citizen who was whisked out of Russia after he fell ill has concluded it’s highly plausible he was poisoned.

Pyotr Verzilov, 30, a member of punk protest group Pussy Riot and publisher of a human rights news website, fell ill a week ago after attending a court hearing in Moscow. He was rushed to a Moscow hospital and was disoriented with dilated pupils on arrival and, as his symptoms progressed, struggled to see, hear and move.

Fearing for his safety, family and friends arranged for him to be taken to Germany on a chartered medical flight on Saturday.

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Dr. Kai-Uwe Eckardt, who heads the intensive care department at Berlin’s Charite hospital, told reporters Mr. Verzilov is suffering from an anticholinergic syndrome, a condition in which the passage of certain neurotransmitters is blocked, the sudden onset of which is strongly indicative of poisoning.

While doctors haven’t yet determined what exactly occurred, they said a poisoning could have resulted from various substances including high doses of some pharmaceuticals and plants that contain particular toxins.

The medical team has found no evidence of anything else that may have caused a sudden and severe illness. Mr. Verzilov remains in intensive care.

Foreign Affairs Minister Chrystia Freeland said she is following the situation very closely and has spoken with Mr. Verzilov’s mother, who accompanied him on the flight to Berlin. Ms. Freeland said nothing about a possible Canadian response but said Canada “will act appropriately.”

“We have assured his family that Canada is here to support him and we are working very closely with him, with his family. Our officials are in touch with them in Germany … this is something we are monitoring very, very closely,” Ms. Freeland told reporters Tuesday.

Last week, Prime Minister Justin Trudeau said reports of the possible poisoning were particularly concerning in light of allegations that Russian agents were behind an attack last March in Britain that targeted Sergei Skripal, a former Russian spy.

Dr. Eckardt said he expects Mr. Verzilov to make a full recovery and hopefully suffer no permanent damage.

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He said Mr. Verzilov, who holds dual Russian and Canadian citizenship, is already communicating with doctors but so far they haven’t been able to question him in detail about his medical history. The rapid onset of symptoms – including high blood pressure and dry mucous membranes – strongly indicated poisoning, doctors said, but it was almost impossible to identify what poison had been used so long after it was administered.

A fellow member of Pussy Riot, Mr. Verzilov’s former wife Nadezhda Tolokonnikova, told reporters at a separate news conference in Berlin on Tuesday that he is “one of the most effective activists that Russia has ever seen.”

Ms. Tolokonnikova said Mr. Verzilov might have been targeted by law enforcement agencies embarrassed by his stunts.

During the World Cup this summer, Mr. Verzilov and other members of Pussy Riot disrupted the final match by running onto the field dressed in police uniforms, an act designed to protest police tactics and to draw international attention to the government of Vladimir Putin. He was sentenced to 15 days in jail.

“No one who is taking part in political activities in Russia right now can really be safe,” said Ms. Tolokonnikova, who herself became a worldwide figure of dissent when she and two bandmates were jailed for performing a song critical of President Vladimir Putin in a Moscow cathedral.

She credits her then-husband for keeping the case in the international spotlight while she was imprisoned in 2012 and 2013. They later divorced, but have remained close.

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She said she believes Mr. Verzilov would likely return to Moscow once he recovers. His father has said he would like to bring his son to Canada to recuperate.

With a report from Reuters