"On Saturday, April 22, at about 9 p.m. [5 p.m. GMT], a 36-year-old Turkish national staying in St. Petersburg on a business visa reported that three individuals attacked him in a subway train following a sudden argument," police said in a statement.
The victim received medical treatment for severe bruising and head injuries.
Police have detained three unemployed men resident near St. Petersburg in connection with the attack, and opened a criminal investigation.
Recent weeks have seen a wave of attacks on non-whites, particularly in St. Petersburg, Russia's second city. Protestors took to the streets after an African student was shot dead in April 7 with a rifle marked with a swastika.
Human-rights groups have raised concerns over what they say is an alarming spread of racist and xenophobic attitudes in the country.
