A man has told police he believes he was knocked out and hospitalised by attackers who then made off with his mobile phone.
The incident, which occurred on Saturday, August 16, took place on the Aileach Road in Ballymagroarty.
Police are keen to hear from anyone who can help establish how the man sustained injuries that required hospital treatment.
At about 9.30pm, the man was walking up Aileach Road on the same side of the road as the bungalows at Ennis Place.
According to a PSNI spokesperson the man felt someone or something strike him to the head and he was rendered unconscious.
He later attended Altnagelvin Hospital where he received three staples. His mobile phone is missing and the man believes it may have been taken while he was unconscious.
Information can be given on the police non-emergency number 101.