The 59-year-old was cycling along Dumbarton Road in Glasgow when he collided with the open door of a parked car and was thrown onto the road.
He was then struck by a Fiat Panda car travelling behind.
Police have appealed for witnesses to the accident which happened near the junction with Crow Road at around 6.40pm yesterday.
The cyclist is being treated for head and chest injuries at the Western Infirmary where doctors described his condition as serious.
Anyone with information is asked to call Police Scotland on 101.