Police are appealing for witnesses who may have seen a hit-and-run.
The woman was discovered in a ditch in Beach Road at just after midnight on 12 February 2024.
It's believed she went for an evening walk at 6pm and was involved in a collision.
Police say the woman is in her 40s and from Cottenham.
She was taken to hospital where she remains in life-threatening condition.
PC Alex Bond, Cambridgeshire Police:
"We believe the victim was involved in a collision but the vehicle didn’t stop at the scene.
"It was dark at the time so the driver may not have known they hit someone.
"I am asking anyone who was driving along that stretch of road yesterday evening to please get in touch if they saw anything or have dashcam footage from the area."
Anyone with information or dashcam footage of the collision, or the moments before or after, are being urged to contact Cambridgeshire Police.