Shortly after 7pm on Monday, October 28, two men picked up bottles of wine from a fridge in the Co-Op store in Fieldmill Road, Bellinge, and made for the exit.
As they tried to leave the manager saw them, prompting the shorter of the pair to strike him in the head with a bottle, causing swelling and bruising.
The pair then ran towards the Deer Leap pub, where the shorter man fell and dropped a bottle, before both ran off.
A Co-op spokesman said: “Fortunately, no one was seriously hurt, however colleagues were left shaken.
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"As a community-based organisation we can see the impact of social issues in our stores, and safety and security is a number one priority for us.
"We have invested millions of pounds in innovative technology to deter crime, including the latest remote monitored CCTV and SmartWater in our ATM’s and kiosks.
"We appeal for anyone who may have seen or heard anything to come forward to police, who are investigating.”
A number of people were around the shop entrance at the time of the incident and police would like to hear from them as they may be able to provide further information about the incident.
The suspect who assaulted the manager is described as a white man, around 5ft 6in, of slim build, in his late teens to early 20s.
He wore a grey hoody, a black jacket with a fur-edged hood worn up, grey jogging bottoms and grey trainers - he also carried a black Nike rucksack on his back.
The second suspect is described as a white man, around 6ft, of slim build and also in his late teens to early 20s.
He wore a red jacket with a white logo on the chest and the jacket hood up, blue jeans and dark shoes.
Anyone who saw the incident or has information about it should call Northamptonshire Police on 101, or Crimestoppers anonymously on 0800 555111.