The incident took place around 9:50pm in Cardross Road, Broxburn on Wednesday 15 August.
A 28-year-old man suffered serious injuries to his neck and was taken to Edinburgh Royal Infirmary for treatment.
Detective Constable Jason Beck of Livingston CID said: “This was a serious attack on a man that resulted in significant injuries to his neck which could have been life threatening.
“We are still conducting inquiries to establish the full circumstances and officers are following a positive line of inquiry.
“We are eager to speak to anyone who may have witnessed the incident or who has information about who was responsible.”
Anyone with information can contact Police Scotland on 101, quoting incident 4064 of the 15th August or contact Crimestoppers anonymously on 0800 555 111