Police were called to Front Street shortly after 11.55am on Monday, December 30, following reports that a man had been punched in the face by another man who was riding a motorcycle.
The attack left the 57-year-old victim with a cut to his eye and a burst nose, and officers took him to hospital for treatment.
An 18-year-old man has been arrested by officers in connection with the incident. He has been released on bail while further enquiries are carried out.
The suspect rode off from the scene following the incident, which happened close to Betfred.
He is described as having bleach blonde hair and was wearing a khaki green puffer jacket with a hood, black tracksuit bottoms, and black Nike trainers.
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Officers investigating the incident are appealing to any witnesses of the incident, or who saw the bike before or after the incident.
A spokesperson for the force said: “Call Durham Constabulary on 101, quoting incident number 135 of December 30 with any information, or contact us online at www.durham.police.uk
“Information can also be submitted anonymously to Crimestoppers on 0800 555 111 or online at www.crimestoppers-org.uk.”