He is accused of participating in an extremist community.
"The court granted the investigator's petition to elect a measure of restraint in the form of detention against I.S. Sergunin," the court said.
Earlier, an RT source reported the detention of three of Navalny's lawyers: Igor Sergunin, Alexei Liptser and Igor Kobzev.
According to the source, Olga Mikhailova, Navalny's main defender, fled Russia abroad. RT published a video of Mikhailova at the airport
* Alexei Anatolyevich Navalny is included in the register of individuals involved in terrorism and extremism.