Two men, both in their 30s, had been having a barbecue in the park when they were approached by two men at about 8pm.
The pair attacked one of the victims, hitting him in the face and knocking him unconscious before kicking him while he was on the ground, before making off with his bank cards.
The second victim tried to intervene and was also assaulted, suffering swelling to his cheek.
Police are asking for the public’s help to identify the man in the CCTV image.
Those with information, or anyone who witnessed the robbery is urged to contact police online via webchat or by calling 101 and quoting incident 27 of July 19.