The incident occurred around 7pm yesterday, Wednesday, March 27, on Mosside Road in Blackburn.
A 51-year-old man was walking in the area when another man exited a black Vauxhall Corsa and attacked him.
The victim was left with a deep cut to his face and was treated by the Scottish Ambulance Service, but did not attend at hospital.
He believes he was attacked with a weapon but did not see what it was.
Inquiries are ongoing to trace the suspect and Police Scotland are urging anyone who can help identify him to come forward.
The attacker was white, around 20, 5ft 8ins tall, of medium build and wearing a dark Stone Island top with a high-peaked cap.
Detective Chief Inspector Paul Batten from Lothians and Scottish Borders CID said: “We are still working to establish the full circumstances surrounding this assault and would ask any members of the public, or motorists, who were in the area at the time, and who witnessed what happened, to contact police immediately.
“It is believed the Corsa was also travelling with a white Vauxhall Astra and anyone who remembers seeing these vehicles before or after the attack should also get in touch.
“Likewise, we are keen to hear from anyone else who believes they may have any other relevant information.”
Those with information can contact Livingston CID via 101 and quote incident number 3598 of the 27th March. Alternatively, an anonymous report can be made to the charity Crimestoppers on 0800 555 111.
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