The suspect entered Esso, in Pershore Road, Selly Park, in Birmingham, at around 7.15pm on March 14.
He picked up a bottle of spirits and a can of beer – and tried to leave without paying.
When challenged by a cashier, he launched into a violent attack.
The victim was left with two head wounds – one which required 14 stitches – as well as bruising to his face, body and arms.
West Midlands Police officers have now released images and CCTV of the suspect in a bid to trace him.
Anyone who recognises him is asked to call West Midlands Police on 101, quoting crime number 20BW/73001G/21.
Alternatively, call Crimestoppers anonymously on 0800 555111.