Gweedore and Donegal player Kieran Gillespie is expected to be out of action for around nine months after sustaining a cruciate ligament injury.
Centre half-back Gillespie suffered the tear in the opening moments of Gweedore's Ulster Club win over Cargin on Sunday.
Gillespie, who had hamstring and hip injuries in recent years, had to be stretchered off.
A club statement said the injury had been confirmed as "an ACL tear.
"Kieran will be a big loss to our current campaign and we wish Kieran all the best in his recovery," said the Gweedore club.
First up, Gillespie will miss Gweedore's Ulster Club semi-final against Crossmaglen on 18 November.
The Donegal champions are likely to welcome back Odhran MacNiallais and Odhran McFadden who missed the win over Cargin because of respective broken finger and dead leg injuries.
Gillespie's injury means he will be unavailable for Donegal's Division Two Football League campaign while the timeframe for his recovery means he is also likely to miss all of the county's championship campaign next summer.