Peel Regional Police said the collision took place just before 8 a.m. at the intersection of Resolution Drive and Steeles Avenue, a large intersection near several big box stores.
The SIU said the officer was driving southbound on Resolution when a pedestrian was struck by the cruiser.
The victim, a 33-year-old man, was taken to hospital with a leg injury. Police said it's unclear how serious the man's injuries are.
SIU investigators are asking anyone who witnessed the collision to contact them at 416-622-1965.
The organization — which probes all incidents involving police in Ontario that result in serious injury or death — said in a news release that it has assigned four investigators, two forensic investigators and a collision reconstructionist to figure out what happened.
Four pedestrians have been struck and killed in the past several days, while several others have been seriously injured.