The victim, a woman in her 20s, was walking home along an underpass beneath the A10 at about 4am on Wednesday (9th December) when she heard footsteps coming behind her.
The suspect is said to have chased the victim before tackling her to the ground and attempting to take her trousers off.
The woman was able to escape after kicking and scratching her attacker, before fleeing along a path in the direction of Station Road, Melbourn.
The suspect, a man in his 30s or 40s, is described as being white, about six foot, blue eyes, with dark hair and a beard.
He was wearing dark sportswear.
Detective Sergeant Bethan Davies said following the incident, police officers will increase patrols in the area.
She said: "I would like to applaud the courage of the victim, both during the incident and also having the bravery to come forward and report the offence to police.
“Although we don't believe anyone witnessed the incident, there may be someone out there who recognises the man's description, or who may have CCTV footage covering the area.
“Any information, no matter how small, could help us build a better picture of the incident and bring the man responsible to justice."
If you believe you can help, please call 101 quoting incident number 37 of the 9 December.
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