The man was driving his green Commodore station wagon east along Erin Street in Queanbeyan on Friday evening, when the car started having mechanical problems.

He pulled to the side of the road outside a nursing home at about 5.30pm to inspect the car.

He noticed a man and woman sitting in a white hatch arguing. He went to the vehicle to offer help, only to be punched in the face by the male driver, who then drove off.

The victim was treated for facial injuries.

The alleged attacker is described as in his mid-20s, Caucasian and about 177 centimetres tall with a solid build and short dark hair.

Anyone who may have witnessed the incident is urged to contact Crimestoppers on 1800 333 000 or Queanbeyan Police on 6298 0555.