Donegal are anxiously awaiting the results of an x-ray on the left knee of All-Star full-back Neil McGee.
The Gaoth Dobhair man had his left knee examined last night to determine the extent of the injury that forced him off after 46 minutes of yesterday's loss to Mayo that leaves Jim McGuinness's team still in danger of being relegated.
"He dislocated his knee cap at the time," said McGuinness.
"They think it might have re-located again itself when he got it straightened up in the shower. We'll just have to wait and see."
Less than a minute after McGee was withdrawn, Mayo netted the game's crucial score.
Cathal Carolan won a vital turnover deep in Mayo territory and corner-back Keith Higgins made a telling incision before Seamus O'Shea fed Michael Conroy, whose effort looped over Paul Durcan and into the net off the inside of the post.
Donegal's task was trickier still when Anthony Thompson was sent off in the 54th minute after hauling down Chris Barrett, just four minutes after first being booked.
Mayo finished well with Colm Boyle on target and substitute Enda Varley scoring twice late in the day to make the win safe, although Donegal were still within touching distance.
Ryan McHugh's first point for the Donegal seniors and Michael Murphy's free kept them with some hope of late salvation, but on a day of mass frustration for the All-Ireland champions they could have no qualms about the final result.
Mayo also finished with 14 men as Jason Doherty picked up his second booking near the end.
Donegal had started well and were 0-4 to 0-1 up by the 17th minute, Murphy and Colm McFadden with a brace apiece.
But Mayo, propelled by the frees of Cillian O'Connor, hit five-in-a-row to lead by two, 0-6 to 0-4, at the break.
With a little more composure and certainly a degree more of a ruthless edge, Mayo could have had more between them.
Paul Durcan got the slightest, but most crucial of touches to deflect a 20th minute goal chance for Doherty round his post.
In the second half, Barry Moran and Seamus O'Shea lorded the centrefield battle and it was from here that the westerners created the platform which led to ultimate victory.
McGuinness meanwhile was left to reflect on a day of wasted possession and poor distribution.
"That is very unlike us," he said. Of more pressing concern, though, was the extent of McGee's injury.
Nine weeks out from their Ulster meeting with Tyrone, the Donegal manager said: "As long as he's alright, we can live with the result."
Mayo: D Clarke; C Barrett, G Cafferkey, K Higgins; L Keegan, TCunniffe, C Boyle (0-1); B Moran, S O'Shea; K McLoughlin (0-2, 1f), AO'Shea, C Carolan; C O'Connor (0-5, 4f), J Doherty, M Conroy (1-0). Subs: R Feeney for O'Connor (54), D Vaughan for Higgins (59), E Varley (0-2) for Conroy (62), Brian Gallagher for S.O'Shea (64), Alan Freeman for Carolan (70).
Donegal: Paul Durcan; Paddy McGrath, Neil McGee, Eamon McGee; Declan Walsh,Frank McGlynn, Anthony Thompson; Neil Gallagher, Rory Kavanagh (0-1);Ryan Bradley, Leo McLoone, Mark McHugh; Patrick McBrearty, Michael Murphy (0-3, 2f), Colm McFadden (0-3, 2f). Subs: Ross Wherity for Walsh (23), Ryan McHugh (0-1) for Bradley (ht), Martin O'Reilly (0-1)for McLoone (ht), Ryan Bradley for N. McGee (46), Martin McElhinney for Wherity (60).
Referee: Marty Duffy (Sligo).