It was confirmed last night (Tue) that neither full back McNamee or the versatile McMahon will feature against the Mourne men.
McMahon has not played for the Red Hands this season, having missed the entire league campaign due to a groin problem.
His efforts to make a comeback with his club were set back when he picked up a calf injury
McNamee picked up a black card in the early stages of the final NFL game against Dublin, but would have been taken off had he not been dismissed, having damaged a shoulder in the incident which led to his departure from the action.
Tyrone also have concerns over Colm Cavanagh and Connor McAliskey.
Midfielder Cavanagh is struggling with a quad muscle problem, while McAliskey picked up a knock while playing with Clonoe last weekend.
Conor Clarke is also back in contention to play against Down in the Ulster opener, having missed the last two league games with a groin strain. He came through a club league game with Omagh at the weekend without any adverse reaction.