Southampton midfielder Morgan Schneiderlin will miss the rest of the season because of a knee injury, manager Ronald Koeman has confirmed.
The Frenchman suffered the problem during the 2-2 draw against Tottenham last weekend, with scans revealing the problem was serious enough to sideline him for up to a month.
Koeman said at a press conference: "Morgan will be out until the end of the season, for four or five weeks."
Southampton head to relegation-battlers Sunderland on Saturday looking to maintain hope of European qualification, currently in seventh place but only a point behind both Spurs and Liverpool.
Schneiderlin had played a central role in Saints' promising campaign, which had earlier seen them up in the Champions League places.
The 25-year-old's performances have seen him linked with a summer move away from St Mary's Stadium, with the likes of Tottenham and Arsenal reported targets, although the club insists he is not for sale.
"He is a key player, so it is disappointing," said Koeman. "It is the ligaments of his left knee and that is a shame because he's out for the last part of the season."
The Southampton manager also confirmed midfielder Dusan Tadic would miss the trip to the north east.
Koeman said: "He is struggling with some groin problems for a long time and we decide now to put him out of the team because he has to recover and be 100 per cent and, if not, he will struggle next season and we don't want that."
Victor Wanyama will be available again following suspension at the Stadium of Light, so Toby Alderweireld could drop back into defence.
Southampton thumped Sunderland 8-0 at St Mary's in October.
Koeman, though, is not expecting another walk in the park against a team fighting for survival under new head coach Dick Advocaat.
"We had unbelievable help from the players of Sunderland. It was so strange. We didn't play really well," he said.
"We scored great goals, but the game of this Saturday will be totally different.
"Sunderland have two home games and they need two wins. That means a lot of pressure and we have to prepare for that."
Southampton also have no intentions of letting Schneiderlin or any other key men leave in the summer.
Koeman said: "We like to keep everybody but we know sometimes it's difficult. But there isn't any serious bid for the player."
It has been suggested Schneiderlin wants to secure a summer move to a Champions League club.
Koeman said: "He is happy (here), but it is up to the player."
Southampton are also keen to tie up defender Nathaniel Clyne on a new long-term deal, the player having been linked with a big-money move to Manchester United.
"We are still speaking with Clyney and his agent, but we have to know it in 10 days now. The club is doing and offering the maximum we can do, then we expect the decision of the player," Koeman said.
"I have spoken to Clyney. He is very happy. Maybe there is some interest, I don't know because nobody has really had a bid for the player, but if I read the press then maybe there is some interest."
Koeman added: "All the players in the Southampton team are happy with how the team are doing but it is football, you never know.
"It is all about interest. We do everything to keep everybody in the team but it is difficult."
