Ki Sung-Yueng could be out for up to two weeks with tendonitis, according to Sunderland head coach Gus Poyet.
The South Korean midfielder - on loan from Swansea City - was left out of Wednesday's 2-2 draw at Manchester City and his absence will come as a huge blow to the club's hopes of Premier League survival.
However, Poyet hopes to have the 25-year-old back sooner rather than later, with Sunderland six points adrift of safety at the foot of the table.
"Nothing serious, but it was getting worse, so we had a good chat, he had an MRI, we talked to the doctor in the national team and it was time to stop," he said.
Fernandinho gave City the lead inside two minutes at the Etihad Stadium before Connor Wickham threatened to completely derail the home side's title hopes by scoring twice in 10 second-half minutes.
However, Samir Nasri's late drive was fumbled by Vito Mannone before trickling over the line, with Poyet quick to defend his goalkeeper.
"That was the hardest part because he's been outstanding," he continued.
"He feels terrible now. It's about feelings and it's about controlling emotions.
"We win all together, we celebrate. When we beat Man United (on penalties to reach League Cup final) all together we were all responsible - him a little bit more.
"That doesn't mean I changed my mind. He needs to recover quick. We need him for Saturday (away at Chelsea)."
|Coach: M. Pellegrini|
for S. Agüero 57'
for Negredo 68'
for Fernandinho 87'
|Police visit Sports Direct over Rangers investigation|
|Guard of honour should spark Liverpool - Lallana|
|Liverpool to sign teenage Portuguese star|
|Thiago would´ve stayed at Barca under Pep|
|Copa Libertadores Review: Tigres advance to quarters|
|Houston Dynamo 0 San Jose Earthquakes 1: Kinnear claims triumphant Texas return|
|Martinez: Everton got carried away during unbeaten run|
|Neymar has flourished with captaincy - Dunga|
|A-League Preview: Victory, City to meet in biggest Melbourne derby|
|Ramos: Real Madrid in box seat|
|´Bale gave Real nothing´ - Keane|
|Hill backs Ramsey for QPR job|
|Ancelotti confident of Real revival|
|Allegri rues late Llorente miss in Juve triumph|
|Juve sent a warning - Pirlo|
|Inverness Caledonian Thistle 2 Dundee United 1: Ofere and Williams keep European dream alive|
|Juventus 2 Real Madrid 1: Spot-on Tevez earns first-leg lead|
|Sturridge hip surgery a success|
|Coloccini calls for unity as Newcastle target survival|
|Doumbia cleared to make Milan trip|
|Harper calls for Hull unity|
|Guardiola not distracted by Barca homecoming|
|No defence can stop Barca star Messi - Guardiola|
|Neuer ready to face Barca strike trio|
|Napoli v Dnipro: Benitez seeks to make experience count|
|Jones ready for United return|
|Injury rules Oscar out of Brazil´s Copa squad|
|Mazinho proud ahead of Barca v Bayern contest|
|Sevilla v Fiorentina: Kolodziejczak confident ahead of semi-final test|
|Skipper Soriano set for Villarreal return|
|Martinez wary of Pienaar risk|
|AFC Champions League Review: Holders Western Sydney out due to last-gasp Seoul winner|
|Barca focused ahead of Pep return - Luis Enrique|
|Messi has ´no problem´ with Luis Enrique|
|Relegated Tranmere appoint Brabin|
|Ujah agrees Werder transfer|
|Magath backs Guardiola to remain at Bayern|
|Mathieu out of Bayern clash|
|Burnley appeal Duff dismissal|
|Setif drawn in Algeria-heavy Champions League group|
|Terry calls for new Drogba deal|
|Saul agrees bumper Atletico deal|
|Arsenal need to finish season strongly - Wenger|
|New Bilbao deal for Gurpegi|
|Pepe puts Morata friendship aside for Champions League match-up|
|Terry: Too long between titles|
|Hazard can be as good as Messi, Ronaldo - Fabregas|
|Carlisle ´deeply ashamed´ about suicide attempt|
|Tevez planning to win Champions League with Juve|
|Blatter ´knows absolutely nothing´ - Maradona|
|Allegri: Ancelotti a smart man|
|Sunderland academy coach to manage Oldham|
|Primeira Liga Review: Braga secure Europa League berth|
|Bruce backing Hull to respond against Burnley|
|Almeria 2 Celta Vigo 2: Bifouma, Zongo inspire hosts´ comeback|
|Arsenal can mount title bid - Wenger|
|Turkish Super Lig Review: Besiktas and Galatasaray remain locked at the top|
|Cagliari 4 Parma 0: Festa revival back in gear|
|Hull City 1 Arsenal 3: Sanchez at the double as visitors close on second|
|Blackpool - Huddersfield game will not be finished|
|Allegri vindicated by Juventus success|
|Russian Premier League Review: Krasnodar close the gap as Zenit slip up|
|Al Ahly dismiss Garrido|
|MLS Preview: Kinnear returns to Dynamo with Earthquakes|
|Ancelotti all out for victory against Juventus|
|Ramires recovering well after sickness|
|Prince Ali would back rival FIFA candidate to oust Blatter|
|Barcelona v Bayern Munich: Guardiola makes Camp Nou return|
|Kruse a target for Wolfsburg - Allofs|
|Fletcher backing Bournemouth to ´surprise a few´|
|Bremen agree deal with Fritz|
|Carver gets Newcastle backing|
|Blaszczykowski suffers groin tear|
|Boateng warns of Barca ´storm´|
|Brouwers agrees Gladbach extension|
|Benzema to miss Turin trip|
|England great Jimmy Greaves suffers stroke|
|Cabaye concerned by bit-part role at PSG|
|Parry: Anfield expansion a major boost|
|Ki targets Arsenal win and seventh spot|
|Pirlo eyes potential Champions League swansong|
|Mourinho rounds on critics after clinching title|
|Henderson: Liverpool can push on without Gerrard|
|Lack of goals a concern for Van Gaal|
|Hard to keep Benteke - Bacuna|
|MLS Review: Sporting KC end Chicago streak, Martins brace furthers NYC pain|
|Copa Libertadores Preview: River eye revenge in Superclasico|
|Garcia lauds ´impressive´ Roma|
|Pavon goal scores him a BMW for a month|
|Boca beat River in Superclasico|
|Inzaghi to blood youth after third straight Milan defeat|
|Blanc urges PSG to ´remain vigilant´|