Shortly before the Russian attack on Ukraine, one of the Kremlin’s top advisers resigned from his post. Now Anatoly Chubais has been hospitalized with symptoms of a neurological disease in a hitherto unknown European country. Two of the Russians’ confidants told the Reuters news agency.

His wife told a Russian journalist that Chubais suddenly felt numbness in his hands and legs. But he can talk, another source told Reuters.

Chubais himself told the Russian journalist that he was diagnosed with Guillain-Barré syndrome, a rare nervous disease. The New York Times reports. The exact reason for his hospitalization is still unclear, but the news of his sudden illness shows similarities to Kremlin opponents who were poisoned.

Chubais has been a well-known figure in Russian politics since the 1990s and an ally of President Vladimir Putin. He oversaw privatization during Russia’s transition to a market economy, became head of Russia’s state electricity monopoly, and took charge of the state-owned technology company Rosnano. He was also the former chief of staff to former President Boris Yeltsin.

He recently served as Putin’s special envoy for relations with international organizations. In March, he left not only this post, but also the country. He gave no reasons, however it was believed that his departure was due to his opposition to the Russian invasion of Ukraine. He is one of the most senior Russian officials to have resigned from Putin’s government since February.

Putin’s spokesman Dmitry Peskov said the news of Chubais’ illness was sad and the Kremlin wished him a speedy recovery.