Officers are appealing for witnesses following an assault on Rushden High Street, close to the West End DIY store.
The incident happened at 3am on Sunday, 26 June following an altercation outside Fate public house.
A man was punched in the face and knocked unconscious after he fell backwards onto the pavement and hit his head, resulting in him needing medical assistance.
A 28-year-old man has been arrested in connection with incident and is currently on bail pending further inquiries.
Witnesses, or anyone with information, are asked to call Northamptonshire Police on 101. Alternatively, they can call the independent charity Crimestoppers anonymously on 0800 555 111.