Sergei Udaltsov, a coordinator for the opposition movement Left Front, was sentenced on October 13 after being found guilty of resisting police.
He told RFE/RL after the verdict was pronounced that he considered it unjust and would therefore start a "dry hunger strike," meaning he would not eat or drink.
Udaltsov's health deteriorated this week and he was taken to a Moscow hospital for treatment. Doctors then released him to recuperate at home.
Udaltsov told RFE/RL he felt normal and his health had "stabilized" after the hospital treatment. He said he was very surprised to have been released three days early.
Udaltsov was one of the organizers of the opposition Day of Wrath protest in Moscow on October 12.
He was arrested that day after he and other Day of Wrath participants tried to march to the president's office to submit their written demands to the presidential chief of staff.
The Moscow authorities gave permission for the Day of Wrath, but only as a gathering, not as a march, which is why police intervened and arrested several activists.
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