Police and emergency services were called to Brooklyn last night following reports of a collision between a car and a pedestrian.
It is believed the pedestrian was struck by a Kia wagon on Geelong Road about 10:35pm.
The pedestrian, who is an unidentified man aged in his mid-20s, was taken to hospital where he remains with life-threatening injuries.
The driver of the Kia, a 39-year-old Kalkallo woman, was uninjured and stopped to assist at the scene.
Westgate Highway Patrol is investigating the cause of the collision and is appealing for anyone with information to come forward.
Anyone who witnessed the crash, or who may have information regarding the identity of the pedestrian is urged to contact Crime Stoppers on 1800 333 000.