Officers received a ‘concern for welfare’ call on the A3023 at its junction with the A27 westbound Havant exit slip at 8.15am.
A Hampshire police spokeswoman said: ‘We were called to the A3023 at 8.15am to a concern for welfare.
‘We attended along with the ambulance service, there were no obvious injuries to him but he was taken to Queen Alexandra Hospital as a precaution.
‘He was by the bridge on the road, not on the slip road.’
Police said the slip road was not closed.