Photo: The Age

Investigators have been told the man was walking on Beach Street on 22 August when he was involved in an altercation with an unknown person about 4.20pm.

The 42-year-old man was knocked unconscious and sustained significant head injuries during the altercation.

He was conveyed by ambulance to hospital in a serious condition.

The offender left the area on a bicycle.

Investigators have released images of a man they believe can assist with their enquiries.

Anyone who witnessed the incident or with further information is urged to contact Crime Stoppers on 1800 333 000 or submit a confidential report at www.crimestoppersvic.com.au.