The 26-year-old was beaten and kicked by the group around 10:51 p.m. after an argument onboard the train at the Monroe station, according to police.
The victim was also hit in the face with a bottle before his attackers ran away, police said.
He was transported by paramedics to Northwestern Memorial Hospital where he was listed in fair condition, police said.
Three males were taken into custody. Area Three detectives are investigating.