Benny Coulter reportedly suffered an ankle break while playing for his club Mayobridge against Bryansford on Monday.
The Down forward and 2010 All Star looks set to miss the Ulster SFC as a result and would be a huge loss to his county.
The Mourne men take on Fermanagh in the Championship opener on 3 June, with Monaghan or Antrim awaiting in the Ulster semi-finals should they progress.
Mourne boss James McCartan also fears Dan Gordon will also miss out with the ankle injury he picked up in the Division One match against Laois a month ago.
