A 28-year-old woman from Brighton suffered head injuries in an attack on the seafront.
She fell to the ground after being punched in King’s Road, near the junction with West Street just before 4am on Bank Holiday Monday (27 May).
The woman was taken to the Royal Sussex County Hospital in Brighton, Sussex Police said.
Detective Constable Paul Clements, from Brighton and Hove CID, said: “The assault happended just before 4am.
“The victim did not know her attacker and was understandably very shaken both physically and emotionally.
“I would appeal to anyone who witnessed the incident and has not yet spoken to officers to please get in touch.”
He urged witnesses to call Sussex Police on 101 or the independent charity Crimestoppers anonymously on 0800 555111.
A 24-year-old Coventry man was arrested on suspicion of assault causing grievous bodily harm (GBH). He has been released on police bail until Saturday 10 August while inquiries continue.