The assault happened at the One Stop Shop, in Newborough and police have today issued CCTV images of a man they are trying to trace.
The thief put sausages, cheese and cider into a bag and headed towards the exit of the shop.
But the store manager tried to stop the offender, who became aggressive and punched him in the mouth.
The victim was left with a cut to his upper lift following the assault, which happened on August 18 at around 12.30pm.
Anyone with information is asked to call police on 101.