Sunderland have ended Jordan Cook's loan at Darlington after he suffered a knee injury this week.
Cook was turning out for the Black Cats' second string under the terms of his youth loan agreement with Darlo, who sit rock-bottom of League Two.
But he was stretchered off and required lengthy treatment after falling awkwardly after just half an hour of the reserves' 1-0 defeat at Burnley at Hetton.
Further investigations revealed damage to his cruciate ligaments. The injury required surgery and Cook is expected to be out for a significant period.