The attack happened in Dryland Street, some time between 4am and 4.30am last Saturday (October 22), after the victim had left the Abacus bar in Horsemarket.
He began a friendly conversation with two men, but shortly afterwards one of the men punched him in the side of the face before both offenders began kicking him on the ground while demanding money from him.
The victim’s mobile phone, which had cash in the flip case, fell out of his pocket during the assault and the two offenders took it before making off.
The offenders were both white, British and aged between 20 and 25.
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Anyone with information can contact Northamptonshire Police on 101.
Alternatively, they can call the independent charity Crimestoppers anonymously on 0800 555 111.