The Province's Special Investigations unit is looking for witnesses to an incident Monday night near Yonge and College.
They say Toronto Police were called around 11:30 p.m. for a report of an armed man.
Police arrived, there was an interaction, and then a short foot chase.
The man was arrested at Yonge Street and Alexander Street. The SIU says he was taken to hospital and diagnosed with a serious limb injury.
The SIU is called in whenever there is a report of death, serious injury or sexual assault allegations involving police.
They're asking witnesses to contact the lead investigator at 1-800-787-8529.