Police were called to the incident outside a hotel in High Street, Penicuik last Saturday, which resulted in two men, aged 22 and 30 being injured.
The 30-year-old man was taken to hospital.
Police have established that a number of people witnessed the incident, and officers are asking them to get in touch.
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They are also continuing to review relevant CCTV footage and have carried out door-to-door enquiries.
Detective Constable Kim Allan said: “A number of people were in this area at the time of the incident and I am appealing to them to contact us.
"At this stage, the motive is unknown for these assaults and it’s imperative we trace whoever is responsible.
"I would ask anyone with information to pass it on, your information could prove vital in our enquiries.”
Anyone with information is asked to call Police via 101, quoting incident number 4316 of 18 June 2022.