Three locals - one aged 15 and two 21 - are said to have attacked the foreigner at a bus stop and were apprehended as they attempted to flee the scene, a police spokesperson said.
The suspects claimed that the brawl, which left the Zimbabwean with some bruises, had started after the foreign student refused to let a young woman take his seat in a bus.
Police said they were checking the suspects' background to establish whether they belonged to a skinhead group or any other local extremist organization.
Extremism and xenophobia in Russia have been in the spotlight following a wave of race-hate attacks across the country and the publication of a report by Amnesty International that slammed the government for not doing enough to combat the problem.
