A 19-year-old was attacked with a broken bottle in Hove Park yesterday evening (Sunday 29 July).
The Brighton teenager was taken to the Royal Sussex County Hospital for treatment to a cut to his left arm.
A 16-year-old girl from Brighton was also attacked during the same incident which happened at about 6.20pm yesterday.
She suffered a bruised face but did not require hospital treatment.
Sussex Police said that detectives were investigating reports that both victims were injured after a dispute with a group of youths south of the tennis courts in the park shortly beforehand.
No arrests have been made at this stage.
Detective Sergeant Helen Paine said: “We would like to hear from anyone who was in the area at the time and saw anything of what happened.
Witnesses can call Sussex Police on 101 or the independent charity Crimestoppers anonymously on 0800 555111.