The 48-year-old was punched in the face as he passed a group of up to a dozen youths at the McDonald’s restaurant on Groathill Avenue, Craigleith, at 3.35pm.
The victim sustained multiple fractures to his left cheekbone in the assault and is understood to be at St John’s Hospital in Livingston.
The gang fled towards the Craigleith Retail Park and are described as being white, male and aged between 12 and 16-years-old.
A police spokesman said: “Officers are keen to hear from anyone who remembers seeing the group prior to, or following the incident.”
Anyone with any information can contact Lothian and Borders Police on 0131-311 3131, or Crimestoppers on 0800-555 111.