At approximately 2.35am on Sunday an officer in High Street, Bedford, was approached by a man who had just been assaulted by a man before having his bank card and phone stolen.
The victim was taken to hospital and an investigation has been launched.
The suspect is described as a white man who was wearing light coloured trousers with a short sleeved top. He was seen to walk through Luddington’s Passage from the High Street and into Ram Yard after the attack took place.
Detective Constable Dave Brecknock, investigating, said: “This was a completely unprovoked attack which has left an innocent man with serious injuries.
“I’m appealing for anyone who witnessed the altercation to get in touch to assist us with finding the man responsible.”
Anyone with information is asked to contact DC Brecknock on 101.