"He is in the general ward. His condition is satisfactory", a spokesperson said.
Earlier, the opposition figure's press secretary said that Navalny was diagnosed with "acute allergic reaction".
A Moscow court sanctioned the arrest of Navalny for 30 days over repeated violation the administrative code on Wednesday as he called for an unauthorised rally to protest the exclusion of several opposition supporters from the Moscow city council race. Judge Valentin Kuleshov said the 43-year-old had repeatedly violated the administrative code by calling the rally to protest the exclusion of several opposition supporters from the Moscow city council race.
Police detained 1,074 people at an unauthorised rally on Tverskaya Street near the Moscow Mayoral building on Saturday. According to law enforcement, about 3,500 people attended the uncoordinated event in the centre of Moscow.