The 54-year-old, who was involved in an altercation with a white van driver on the A8, at Renfrewshire, died in hospital at the weekend.
It is understood he may have been suffering from a head injury. Police have appealed for help in trying to piece together what happened.
The incident took place on the A8 near Langbank at 2pm on Saturday July 7.
Police said the man was driving a black Ford Mondeo westbound, when he became involved in an altercation with the driver of a Ford Transit van.
Both vehicles stopped and the Mondeo driver got out of his car to speak with the other driver. The man was treated for minor injuries and released from hospital later that day.
However, last Thursday he was readmitted to the Royal Alexandra Hospital, and he died on Saturday.
A post-mortem examination is due to take place. Police believe motorists, who were travelling on the Glasgow to Edinburgh road at the time of the altercation, may help solve the mystery.