Moorabbin Highway Patrol officers are appealing for witnesses following a crash in Hampton last Sunday.
Investigators have been told a 50-year-old Hampton man was located unconscious by a passer-by on the side of Karoola Street about 6.10pm on 13 December.
It is believed the man was riding his black electric scooter north bound on Karoola Road.
The passer-by told police he found the man lying on the side of the road, approximately 10 metres north of Bayside Crescent.
It is not known how the man came to fall from his scooter and police are appealing for anyone who was in the area at the time and may have seen the man riding along the road to contact them.
He was transported to hospital with life-threatening injuries where he remains.
Officers have canvassed the area for CCTV however they are yet to locate any information that can assist with the investigation and lead them to identify how the man came off his scooter.
Police would like to speak to anyone who may have dash-cam footage of the man riding his scooter or with information regarding the incident to contact Crime Stoppers on 1800 333 000 or submit a confidential crime report at www.crimestoppersvic.com.au