The incident happened on the Erganagh Road in Omagh last night, Friday, July 7.
Inspector Glen Latimer said: “Police attended the scene at approximately 10.45pm.
“The man had sustained serious head injuries and was receiving treatment from ambulance staff at the scene before being taken to hospital.
“I am appealing to anyone that may have witnessed any suspicious activity in the area at the time particularly regarding the movements of 2 Quad motorbikes to contact Omagh Police Station on the non-emergency number 101, quoting reference 1438 of 07/07/17.
“Or, alternatively if someone would prefer to provide information without giving their details they can contact the independent charity Crimestoppers and speak to them anonymously on 0800 555 111.”
Police say the Erganagh Road has now reopened between Rylagh Road and Glenpark Road following an investigation of the scene.