The boy was kept in hospital overnight after the attack, which aggravated an existing medical condition.
The incident happened on Sunday just after 10pm, when the boy and his 10-year-old brother, who are Asian, were walking in Brockburn Road, Pollok, Glasgow, after visiting an aunt.
The victim made his way home and was taken to hospital by his parents. He was discharged yesterday.
Police are hunting for the attacker, who was a white boy, aged about 15 or 16.
Meanwhile, police in Edinburgh are investigating after a 34-year-old, from Pakistan, was racially abused by six people as he went to a shop in Wester Hailes.