Moorabbin Highway Patrol is appealing for witnesses after a collision in Chelsea Heights on 19 February.
Emergency services were called to the corner of Edithvale Road and Egret Drive at 8.07pm after a motorcycle collided with a vehicle.
Investigators believe the motorcycle, a black Suzuki, was travelling southwest on Edithvale Road prior to the collision.
The rider sustained serious injuries and was transported from the scene by paramedics to hospital.
The driver of the vehicle was uninjured and remained at the scene.
Police are continuing to investigate the circumstances surrounding the incident.
Anyone who witnessed the incident or has dashcam footage is urged to contact Crime Stoppers on 1800 333 000 or submit a confidential report at www.crimestoppersvic.com.au.