Sunderland's hopes of avoiding relegation trouble were dealt a double blow on Wednesday when skipper Lee Cattermole and top scorer Steven Fletcher were ruled out for the remainder of the season with injuries.
Midfielder Cattermole has knee surgery on Wednesday while Fletcher damaged ankle ligaments playing for Scotland.
The Premier League club's website said it was not known whether Fletcher, who has scored 11 league goals this season, would require surgery.
Sunderland are four points above the bottom three in 15th place and host runaway leaders Manchester United on Saturday.
Winger Adam Johnson admitted Fletcher and Cattermole will leave sizeable holes in the squad as their team-mates prepare for a run of fixtures which sees them take on United, Chelsea, Newcastle and Everton in quick succession.
He told Sky Sports News: "Catts is obviously a big part of the team. Drive and commitment is his game.
"Fletch has proved himself this season. Without his goals, we would be in a lot worse position. He's going to be a big miss for us.
"I think it's important for the whole team to step up now and put the performances in we know we are capable of.
"It's important someone gets the goals with Fletch missing because we haven't scored that many or created many chances. When we get them, it's important to put them away.
"I think Danny is a couple of games away from getting a good run.
"It's been so frustrating because we have got some really good players. We haven't had the results and have struggled massively at times.
"All the lads are really frustrated, but we have got to keep working hard and hopefully it will come."