Avon and Somerset Police are investigating a fail to stop collision on a roundabout at the junction with the A367 and A362 in Radstock on Friday afternoon.
A silver car, possibly a VW Passat or VW Golf estate, was in collision with a motorcyclist at about 5.10 p.m., causing her to fall from her bike.
The driver initially got out of the car, but then left the scene on the A367 towards Peasedown St John.
The motorcyclist was taken to the Royal United Hospital for treatment.
The driver the police would like to trace is described as white, in his thirties, with blond hair. He may have had piercings and was wearing an orange reflective vest/waistcoat.
If you saw this collision, or recognise the description of the driver, please call PC Barbara Salvage on 101 and give the call handler the reference number: 5217106130.