The forward suffered a knee injury in training on Sunday, while the fear is he may have suffered cruciate ligament damage.
The Glenullin man will miss the Ulster SFC final on Sunday, although if Derry’s worst fears are realised he will miss the rest of the season at least.
He is having a scan today to discover the extent of the damage.
His brother Paddy Bradley, who himself is out with a cruciate injury, said Eoin suffered the injury in training.
‘He still has to go for a scan but there’s something seriously wrong with it and he’s 90% certain it’s gone.
‘It was the usual thing. He was going for a ball in the training game and was turning when the defender came in and made some contact.’
Donegal manager Jim McGuinness has not reported any injury worries apart from Naomh Conaill man Leo McLoone who was injured in a club game.