Veteran human rights campaigner Lev Ponomaryov was rushed to the hospital after being detained at an unsanctioned opposition rally against Mayor Yury Luzhkov.
Ponomaryov, 68, said doctors had diagnosed him with high blood pressure and hooked him up to an intravenous drip after admitting him Thursday evening, Interfax reported.
He had expected to remain in the hospital for 10 days, but told The Moscow Times on Sunday that he was feeling much better and hoped to return home Monday.
Ponomaryov, chairman of the For Human Rights movement, was a co-organizer of the "Day of Wrath" rally, during which demonstrators accused Luzhkov of being responsible for the capital's unpreparedness for this summer's record heat wave and demanded his resignation.
Police detained 35 protesters.
Sergei Udaltsov, another co-organizer of the rally, was sentenced to four days in jail for “ignoring lawful demands of the police,” Interfax said. Udaltsov said Friday that he would stage a hunger strike for the duration of his detention.