David Moyes has spoken of his disappointment after losing Duncan Watmore for the season through injury.
Watmore will miss the rest of the campaign after suffering cruciate knee ligament damage in the 2-1 win over Leicester City at the weekend.
The livewire forward, who Moyes described as "terrific" in recent weeks, was carried off the pitch on a stretcher and scan results confirmed the club's worst fears.
He will now miss the rest of the campaign.
The England Under-21 international, who was enjoying one of his best games of the season, was carried off following a challenge by Foxes’ defender Christian Fuchs in the latter stages of the match.
Moyes said: "It is sad news because he is a great boy.
"Duncan has been terrific for us so he didn’t deserve that, but he will come back.
"These injuries are happening more regularly now, players are coming back, surgeons are better, so we look forward to Duncan returning.
"But it will probably not be until the start of next season now."
Watmore has been a regular under Moyes this season and has linked up well with Victor Anichebe and Jermain Defoe in the club's recent run of three wins in four Premier League games.
His is the latest in a long line of injuries for Sunderland this season.
Watmore’s injury follows long-term injuries to Paddy McNair and Lynden Gooch, while Lee Cattermole is also out for up to four months with a hip injury.
Gooch doesn't need an operation on his ankle injury but is still expected to be out for between two and three months.