The incident took place outside Angus O'Malley's Sports Bar, in The Valley area of Selkirk, at around 1am on Sunday, November 21.
The victim, a 38-year-old man, was taken to nearby Borders General Hospital for treatment of serious injuries.
Detective Constable Liam Myers said: “We’re appealing to anyone who was in or around The Valley around the time of the incident, or has any information which could assist our enquiries, to please come forward.
“You can call police on 101, quoting incident 0266 of 21 November. Alternatively, please call Crimestoppers on 0800 555 111, if you wish to remain anonymous.”