The air ambulance was called to Worthing following reports of an ‘accidental injury’ at 10.59am.
It landed in a field near Sompting.
The KSS spokesman added: “The man was treated by our paramedics before being taken to the neurological unit at the Royal Sussex County Hospital, in Brighton, by road ambulance.
“Air ambulance paramedics, alongside South East Coast Ambulance Service Paramedics accompanied the injured man to hospital.
“The man suffered head injuries in a fall.”
The incident is thought to have involved a tractor but Sussex Police could not provide further detail.