The incident took place on Sherbrooke Street East between 36th and 39th avenues.
Police spokeswoman Const. Lynn Duncan said two cars were headed east when one cut off the other.
The victim stepped out of his vehicle to confront the other driver, who struck the man with his car.
The injured man was taken to hospital in critical condition with serious head injuries.
The other driver was placed under arrest and faces charges of aggravated assault with a vehicle.