A 53-year-old man has been taken to hospital after being found by police with a head injury in Pelham Street, Hastings.
It happened shortly before 9pm on Sunday 10 April.
An investigation established that the man had been assaulted earlier in the evening in Wellington Place, but police are unsure whether he sustained the head injury during the attack.
A 35-year-old local man known to the victim has been arrested on suspicion of causing grievous bodily harm with intent and released on conditional bail while enquiries continue.
Detective Inspector Simon Dunn said:
"The assault happened in a busy area of Hastings town centre on a Sunday evening, and we believe there were lots of people in the vicinity at that time and therefore a high likelihood that someone would have witnessed the incident.
"We are asking anyone who saw what happened, or who may have captured any relevant CCTV or dash cam footage from the area, to please get in touch.
"This was an isolated incident involving people known to each other, and we believe there is no threat to the wider community.
"Members of the public can expect to see a continued police presence in the area while our enquiries are ongoing."
Anyone with information is asked to contact police online or by calling 101 quoting Operation Canford. Alternatively, you can contact the independent charity Crimestoppers anonymously on 0800 555 111.
Overnight Closures For A22 Forest Row Road Improvements
Brighton Defence Manufacturer's Controversial Planning Application Likely To Be Heard
Over £2.4m Approved For Worthing School Support Centre
Section Of M25 To Close Again Tonight - As Drivers Warned Not To Get Complacent
Plans For 800 New Horsham Homes Refused
Over 200 Co-Living Flats Approved For Brighton
Appeal Following Assault In Hastings
Road Closed As Armed Police Attend Incident In Worthing
Lewes District Council Placed In Planning Special Measures