Alexei Navalny is a Kremlin critic who was poisoned in 2020.
Many Western countries say Navalny was poisoned with a nerve agent, but the Kremlin has denied any role in his illness and has said it has seen no proof that he was poisoned.
He is due to spend a little over 2-1/2 years behind bars, according to his lawyers, one of whom, Vadim Kobzev said on Twitter he had been moved from his Moscow jail.
Amnesty still believes that Navalny should be freed from jail.
Navalny was arrested last month on his return from Germany following treatment for poisoning, in Siberia, with what many Western countries say was a nerve agent.
While the repressive power of intimidating, poisoning, and imprisoning Alexey Navalny comes from the Kremlin, perhaps the more decisive power is anchored in the Russian minds.
The report stated that the doctor, Sergey Maximishin, died "suddenly" and noted the hospital did not mention cause of death. He was 55-years-old.
Navalny's allies called on their supporters to immediately protest against the ruling in central Moscow.