Emergency services were called to Church Street, outside Sheffield Cathedral, just before 5.30pm, and at least three police vehicles and an ambulance attended the scene.
A South Yorkshire Police spokeswoman said a 14-year-old boy had reportedly been assaulted by at least two other people.
She said the nature of his injuries were not known at this stage but he was conscious, breathing and talking to paramedics.
She added that there were no reports of any weapons being used, there was no information about the suspects at this stage and no one had been arrested.
Anyone with information is asked to call police on 101.