The 26-year-old was walking along St Edmunds Road, Northampton, between 3pm and 7pm on Tuesday, May 31 when he was hit on the back of the head and knocked unconscious.
As he lay on the ground a number of his personal item were stolen. He was later taken to hospital.
Officers would like to speak to anyone who may have witnessed this incident or who went to the aid of the victim after it happened.
Police would like to speak to anyone who may have been in the St Edmunds Road area of Northampton, on Tuesday, 31 May and who may have any information about this incident.
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Witnesses or anyone with information can contact police on 101 or Crimestoppers anonymously on 0800 555 111.