An appeal has gone out for witnesses to a collision during the RideLondon event on Sunday (July 29).
Thousands of cyclists, including many from Sussex, take part in the annual event.
During the morning a volunteer marshal suffered serious injuries in a collision in Leatherhead.
The incident occurred at around 11.15am in Epsom Road at a crossing point near the junction with The Crescent and Leret Way.
A female rider collided with the marshal who was taken to hospital, where she remains in a stable but serious condition.
Surrey Police says they are appealing for the rider to come forward, or for anyone who can help to identify the rider to contact us.
Anyone with any information, photographs or video footage of the area leading up to and including the incident is asked to call Surrey Police Serious Collision Investigation Unit on 01483 639922, quoting reference PR/P18181165.