The robbery happened at about 1.30am after a 46-year-old man was walking away from the machine at the post office on Broadway, Heanor.
He was grabbed from behind and dragged to the ground, hit on the head and had his wallet stolen on Friday, October 31.
The raiders are thought to be in their late teens or early 20s, with one wearing a blue hooded top.
The victim was treated at the Queen’s Medical Centre in Nottingham for facial injuries.
Anyone with information can contact DC Jim Mitchell on 101.