A spokesman for Dumfries and Galloway Constabulary said: "Traffic flow was heavy at the time in the area of the incident.
The assault took place when the victim pulled up at a set of temporary traffic lights on the Gretna to Stranraer road.
Three men got out of the car behind, walked up to his vehicle and attacked him.
He had to be taken to Dumfries Infirmary for treatment after the incident on Friday evening.
And while the victim was not badly injured, police said they are treating the incident seriously.
A spokesman for Dumfries and Galloway Constabulary said: "Traffic flow was heavy at the time in the area of the incident.
"Police would like anyone who may have witnessed the incident or have information to contact us."
The three men - who are believed to have been in a burgundy or dark coloured vehicle - carried out the attack near Rockall Mains, Collin, about two miles east of Dumfries.
Police said the driver was described as 5ft 10in tall, of medium build and with dark hair. He was wearing a lot of jewellery, a red T-shirt, blue jeans and trainers.
The second man was said to be about the same height, aged between 25 and 30, with short cropped fairish hair. He was of medium to light build and was wearing a cream coloured top and jeans.
The third man was thought to be wearing a baseball cap.