The incident occurred on Svenshögsvägen, at the height of Fäladstorget, in Lund on Saturday night.
The perpetrators, four young men described as being between eighteen and twenty years old, attacked the bus driver who was driving the city bus, with blows and kicks.
The perpetrators then left the scene on foot.
- I do not know why they attacked.
The investigation must show that, says the police's spokesperson Rickard Lundqvist.
One person could be arrested in the immediate area and the search for the other perpetrators continues.
The bus driver is injured, but did not need immediate care.