The incident happened at around 3.45pm as the man was standing at the bus stop opposite the post office in Ramsey Road. A spokesman for Cambridgeshire police said: A man headbutted the victim, leaving him with a serious but not life threatening head injury that required hospital treatment. Detectives are treating the attack as an isolated incident. No arrests have currently been made. Anyone with information about the incident or witnessed the assault should contact PC Emma Garwood on 101 or Crimestoppers, anonymously, on 0800 555111.