Photo: The Age

Officers have been told a 51-year-old Toorak man was crossing Toorak Road at Chapel Street about 10.45am.

The pedestrian has become involved in an argument with a truck driver which has turned physical.

The 51-year-old man was rendered unconscious before the driver of the truck got into his vehicle and drove off.

Investigators wish to speak to anyone who witnessed the incident, particularly anyone who witnessed the initial incident at Toorak and Chapel.

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