Following the verbal exchange, the cyclist punched the motorist in the face through the car's open window, then rode away.
The victim was driving a white Land Rover. The cyclist, aged around 50 and of corpulent stature, spoke French. He wore red cycling gear and a white helmet, and rode a racing bike.
The incident took place on Rue de la Gare in Clemency, at 11.30am on 30 July.
Anyone with information relating to the incident should contact Käerjeng/Péiteng police on (+352) 244-561000 or police.bascharagepetange@police.etat.lu.
