Emergency services raced to the scene shortly before 1pm on the eastbound carriageway of the busy motorway.
Police said the man was taken to hospital. His condition is not known.
It is not yet known how the man came to be on the road.
A Police Scotland spokeswoman, said: "At around 12.55pm, we received a report of male being struck by vehicle on the M8 near to Junction 5.
"Officers attended and the man was taken by ambulance to Wishaw General Hospital."