Officers are appealing for witnesses to an assault which took place on Bristol Road in Gloucester at around 4.35pm on Tuesday afternoon (17 December).
It was reported that a teenage boy was waiting to board a number 12 Stagecoach bus which had stopped near to Aldi and Kwik-fit when he was approached by three boys.
The group attempted to stop the victim from getting onto the bus before he was punched in the face by one of them.
The victim sustained a fractured jaw which required hospital treatment as a result of the attack.
The teenager who punched the victim was described as being white, around 6ft tall and of a stocky build. He was wearing an all-black outfit which consisted of a jumper, jeans and coat.
Officers believe that a number of people who were on the bus may have witnessed the assault taking place and are asking anyone with information to come forward.
One particular person that officers would like to hear from is the driver of a car that was behind the bus at the time of the incident, it is believed that they pulled up alongside the bus to offer assistance.
Anyone who witnessed this taking place or has information is asked to call 101 quoting incident 335 of 18 December.