MOSCOW — Aleksei A. Navalny, the imprisoned opposition leader who returned to Russia this year despite an earlier attempt on his life, is in deteriorating health with unexplained ailments and has received substandard medical care, his lawyers said on Thursday.
Prison doctors moved Mr. Navalny, 44, to a hospital for tests on Wednesday but offered no explanation for his complaints of severe back pain and numbness in one leg, and then returned him to the penal colony east of Moscow, said his lawyer, Olga Mikhailova.
“His health is extremely unfavorable, and every day gets worse,” she said in an interview after meeting Mr. Navalny in prison on Thursday. His right leg has numbed to the point he cannot put weight on it, she said. “We are afraid for his life and his health.”
Mr. Navalny collapsed into a coma on an airplane flight last August and was medically evacuated from Russia to Berlin. After extensive tests there, both the German and French governments, and international chemical weapons specialists, confirmed that he had been poisoned with a Soviet-designed military nerve agent, Novichok.
Prison doctors are not qualified to treat him, Ms. Mikhailova said, and she has filed appeals to move him to Moscow to be examined by a specialist. “His condition is worsening, not improving, with the treatment he is getting in prison,” she added.
His condition has been exacerbated by sleep deprivation, she said, with guards awakening him hourly, ostensibly to confirm his presence in the prison barracks, as he is classified as a flight risk.
After his poisoning, Mr. Navalny and the open-source investigative group Bellingcat studied phone records of Russian security service agents and other clues to reconstruct what they called an attempted assassination.
Mr. Navalny said the poison, which can be lethal to the touch, had been applied to the inside of a pair of his underpants. It was the same class of nerve agent that sickened several people in England and killed one of them in 2018, in what western intelligence agencies said was a failed attempt to kill Sergei V. Skripal, a former Russian spy.