Police say the incident happened when a man was crossing Fourth Avenue near Robinson Street at about 12:45 a.m. Friday.
The officer is a member of the RPS investigative services division and was driving an unmarked police vehicle.
Police say the man suffered non-life-threatening injuries and was taken to hospital by EMS.
The man is in stable condition, police say.
Anyone with information is asked to contact police at 306-777-6500 or Crime Stoppers at 1-800-222-8477.