The 43-year-old man was robbed between midnight and 1am on Tuesday 11 November 2014, on Valley Road, near the junction with Central Drive.
The victim walked up Lascelles Lane, away from East Road before turning onto Valley Road. As he reached the junction for Central Drive he was approached from behind by at least two people, who knocked him to ground and violently assaulted him before stealing his money.
As a result of the robbery he suffered a fractured skull, a broken wrist and a chest injury. The victim was admitted to James Cook Hospital, Middlesbrough, where he has undergone surgery for his injuries. He currently remains in hospital in a comfortable condition.
Detectives are still keen to trace a couple who were walking a dog on Lascelles Lane just before the robbery occurred.
Detective Constable Michelle Waite, of Northallerton CID, said: This was a nasty and vicious robbery, which has left the victim needing surgery.
I am certain that someone will know who is responsible for this shocking incident and I urge them to contact the police immediately.
I am also still keen to speak to the couple who were walking a dog as they may have seen someone acting suspiciously around the time the robbery occurred and ask that they get in touch as soon as possible
This robbery is not being linked to any other incidents of a similar nature in the town, which have occurred in recent weeks.
Anyone who can assist with this investigation should contact Northallerton CID on 101, select option 2 and ask for Michelle Waite.
Or call Crimestoppers anonymously on 0800 555111, quoting reference number 12140195470.