Three men have attacked the Parnas opposition party regional leader in the city Ulyanovsk, east of Moscow, the Meduza news website reported Tuesday.
Alexander Bragin, an advisor to the city's governor, was leaving his house when he was was struck in the back of the head and knocked to the ground, the Interfax news agency reported. Two other men joined the attack and began to beat him, Bragin said.
The men fled when Bragin's neighbor saw the attack and shouted for help.
The activist was taken to the hospital, where he was diagnosed with mild head trauma and back injuries.
Local police say that pre-investigation into the attack has begun, Meduza reported.