It happened at about 11.15 pm near to the Ramhill at Castle Douglas.
A 48-year-old man from Birmingham was travelling east on the road when he was overtaken by an articulated lorry which pulled up sharply in front of his white Mercedes Sprinter van.
When the van driver stopped, the lorry driver alighted from his vehicle, approached the victim and began to assault him.
Nothing appears to have been said by the attacker and the victim as a result was left with a sore face and in a shocked condition.
The driver of the lorry then left the scene and the victim contacted the police.
Officers are now keen to trace the lorry driver, who is described as between 40/50 years old, of stocky build with a beer belly. He was about five foot eight tall and had short grey hair, a goatee beard and moustache. He was wearing a red and white vertical striped t-shirt, jeans and safety boots.”
PC Callum Jardine said: “The victim received some cuts to his face as a result however did not require medical attention. We want to hear from anyone who may have been on the A75 near the Ramhill around this time to get in touch if they saw anything which might help us in this investigation.
“The victim was unable to indicate why this assault might have happened. It may be that a second articulated lorry, not further described, stopped at the scene of this attack at the time and we would like to speak to the driver of that lorry.”