Sunderland midfielder Paddy McNair faces a lengthy spell on the sidelines after rupturing his anterior cruciate ligament.
The former Manchester United midfielder suffered the injury in the first half of Saturday's win over Hull City, but played on until the 88th minute when Donald Love came on to replace him.
"Paddy McNair has been ruled out of action after rupturing his anterior cruciate ligament," a statement on the club's official website read.
"The Northern Ireland international, who joined Sunderland from Manchester United in the summer, suffered the injury during the club's 3-0 win over Hull City on Saturday. The incident occurred in the 42nd minute as the midfielder closed down Curtis Davis on the edge of his own penalty area.
"McNair, 21, faces a lengthy spell on the sidelines but will now focus on returning to action as quickly as possible."
McNair has made 12 appearances in all competitions for Sunderland this term, scoring twice.