Thames Valley Police is appealing for witnesses to a serious crash in Haversham, north of Milton Keynes.
The incident happened in High Street at around 11.20am on Saturday.
A motorcyclist travelling along High Street fell from his vehicle, a red Yamaha XV, and suffered a serious leg injury which was treated at Milton Keynes Hospital.
A green Austin Maestro estate was seen by the motorcyclist at the scene and the driver of this car may be able to help police with their investigation.
PC Neil Stephenson, from the Milton Keynes Road Policing Joint Operations Unit, said: “I am keen to speak the driver of the Maestro, or anyone who can help me identify the driver of that vehicle.”
Anyone with any information should contact PC Stephenson via the Force Enquiry Centre on 101.
If you don't want to speak directly to the police you can contact the independent charity Crimestoppers anonymously on 0800 555 111 or online at www.crimestoppers-uk.org. No personal details are taken, information is not traced or recorded and you will not go to court.