Sunderland's Paddy McNair will miss the rest of the season after rupturing his anterior cruciate ligament, manager David Moyes has announced.
McNair, who can play in defence or midfield, suffered the injury in the 42nd minute of Saturday's 3-0 Premier League home win over Hull as he closed down Curtis Davies, although he did not come off until the 88th minute.
Moyes said: "We won't see him again this season and all we can hope is getting him right for the start of next season.''
The 21-year-old Northern Ireland international has made 12 appearances for Sunderland since joining from Manchester United over the summer. He has scored two goals for the Black Cats, both in the 2-1 EFL Cup win at QPR in September.
"I think he'd just started to find his way in the Premier League -- even though he had experience at Manchester United -- and the games he was having were bringing him on and giving him confidence,'' Moyes told Sunderland's website.
"He probably won't have his operation for over a week because he's got a cut on his knee and they can't operate while there is an open wound, so we have to wait until that heals so it might be a week or two.''
The setback for the Wearside outfit comes at a time when their league campaign has just begun to pick up.
The victory over Hull was the second win in a row for Moyes' 19th-placed side, who had failed to take maximum points in any of their previous 10 games this term.
Confirmation that Paddy McNair is out for the season & will miss the World Cup qualifier against Norway in March. ☹️ #GAWA https://t.co/TSonNRQwBX
- Northern Ireland (@NorthernIreland) November 23, 2016
As well as Sunderland's continued efforts to move away from the relegation zone, McNair will also be absent for Northern Ireland's World Cup qualifier against Norway in March.
As the news of the knee injury emerged, messages of support for McNair were posted on Twitter from the official accounts of both Northern Ireland and Manchester United.
The message from his national team said: "Paddy McNair has suffered a cruciate ligament injury & is expected to miss the rest of the season. Get well soon Paddy!''
United's message said: "Everyone at MUFC wishes you a speedy recovery, Paddy!''