The victim is in a stable condition in the Royal Sussex County Hospital after being seriously injured in a confrontation in Portslade on Saturday.
A 15-year-old boy from Hove was held on suspicion of attempted murder and causing GBH with intent.
An 18-year-old man from Portslade was arrested on suspicion of affray.
Both have been bailed until 18 November.
A 16-year-old boy from Portslade, also arrested on suspicion of attempted murder, remains in police custody.
Sussex Police said emergency services were called to Abinger Road at 17:17 BST where a group of youths were gathered in the car park of the Co-op store.
Two teenagers arrested after a 16-year-old boy suffered "potentially life threatening injuries" in a stabbing in Brighton have been released on bail.