The attack happened in Bangor’s Ward Park on Saturday evening, May 7.
The man, aged in his 20’s, reported that as he walked through the park sometime after 8pm he was struck in the face by a man armed with an unknown object.
He was knocked unconscious and had money taken from his wallet.
The man has since been treated in hospital for a broken jaw.
Detective Sergeant Little has appealed to anyone with any information about this incident or who saw anyone acting suspiciously in the area of Ward Park on Saturday night to contact detectives in Bangor on 101 or Crimestoppers anonymously on 0800 555 111.