The incident happened near Plean at around 12.15pm yesterday afternoon.
A black coloured Yamaha motorbike collided with a grey coloured Volkswagen Tiguan at the crossroads of Roman Road, with Cadgers Loan.
Emergency services attended and the 21-year-old rider of the motorbike was taken to the Queen Elizabeth University Hospital by air ambulance with critical injuries.
The road was closed for six hours whilst enquiries were carried out.
Sergeant David Marr, Forth Valley Roads Policing Unit, said: “We are continuing our enquiries to establish exactly what happened here and would appeal for anyone who was in the area, who may have information that can help us, to come forward.
“If you have dash-cam footage or seen either of these vehicles prior to the incident, we would again urge you to get in contact.”
Contact Police via 101, quoting incident number 1663 of Saturday, 5 June, 2021.