A 29-year-old woman was attacked on her way home from buying groceries in Preston.
Police said it happened at around 11pm on Monday on Ripon Street near to Garstang Road, Preston.
It is believed that two men approached the woman and demanded that she hand over her handbag but she refused.
The attackers then pulled her to the ground and one of them threatened her with a knife.
A passer-by shouted out to the attackers who then ran off and dropped the victim’s bag which has since been recovered.
The two attackers made off on foot in the direction of Moor Park. The victim was left with cuts and grazes to her face, arms and legs.
Officers are keen to trace the man who intervened and are appealing for him to come forward as they believe he may hold vital information about the incident. He is described as a tall white male.
The two offenders are both described as Asian men.
The first offender is believed to be aged around 26 to 28 years old, around 5ft 6in tall, of medium build and spoke with a local accent.
He was wearing a dark duffle-type jacket, black tracksuit bottoms, a black woollen hat and gloves.
The second offender was slightly taller than the first and of a stocky build. He had a goatee style beard and was dressed in black clothing.
DC Steve Gilmore of Preston CID said: “This was a vicious and nasty attack on a young woman and we would urge anyone with any information at all to please come forward. We are particularly keen to talk to the man who ran over and managed to scare off the attackers and we would encourage him to come forward.”
Anyone with information about the burglary or about the offenders can contact Preston Police on 101 quoting log reference 332 of December 8.