Transit Crime Investigation Unit detectives are investigating after a man was attacked on a Lilydale bound train in September.
Officers have been told a man approached the victim, who has autism, on the train between Ringwood and Lilydale stations about 7.30am on 23 September.
The man told the victim to shut up before throwing him on the ground.
He punched and kicked the victim on the floor before getting off the train.
The 31-year-old Wantirna man received bruising and significant mental stress because of the assault.
Investigators have released images of a man they believe may be able to assist with their enquiries.
The man is described as being of Caucasian appearance, mid 30's, bald head wearing a black cap with a white motif, black jumper, black puffer vest, black tracksuit pants and black runners. He was riding a dark coloured mountain bike.
Anyone with information that can assist investigators is urged to contact Crime Stoppers on 1800 333 000.
