Police were called to Brecknock Road, N7 at around 16:20hrs on Sunday, 16 June, following reports of a fight in progress.
Officers and London Ambulance Service [LAS] attended and found a 15-year-old male with a slash wound to the face.
The injured boy was taken by LAS to a north London hospital for treatment – he has since been discharged.
A 25-year-old man was arrested on suspicion of grievous bodily harm [GBH]. He is currently in police custody.
Officers from Central North Command investigate. Enquiries continue.
Anyone with information is asked to call 101 quoting 5270/16June, tweet @MetCC or call Crimestoppers anonymously on 0800 555 111.