Officers say the victim was travelling towards Cross Hills at about 7.15am when he was forced to stop in the layby by a silver Ford Transit. The van driver apparently got out of his vehicle and approached the victim with what appeared to be a piece of wood. "The victim drove away fearing for his safety," said a police spokesman.
The Transit had a possible registration of MK63 DSV.
Anyone with information is asked contact PC James Dykes at Cross Hills Police Station on 101.