Charlie Wyke's knee ligament injury is set to keep him out for up to three months, Jack Ross has revealed.
The Sunderland striker was injured in a collision with Burton Albion keeper Dimitar Evtimov in the 2-1 defeat at the Pirelli Stadium last weekend, with Wyke stretchered from the pitch.
Scans revealed he had suffered knee ligament damage in his right knee, the same injury he arrived at the club with in the summer.
He doesn't require surgery but currently has his right knee in a brace and Ross fears he could be out for up to three months.
It leaves Ross relying on 19-year-old top scorer Josh Maja and Jerome Sinclair, with Chris Maguire also providing support in attack.
Sunderland are not in a position to dip into the free agent market to replace him with the club's wage bill high after they failed to move on the likes of Didier Ndong, Lee Cattermole and Bryan Oviedo.
Speaking at his pre-match press conference, on Wyke, Ross said: "We are now looking at nine to 12 weeks [out], he has some ligament damage.
"It doesn't require surgery but he will be in a knee brace and then working for fitness from there.
"I feel for him, he has suffered the same sort of injury. A separate injury but on the same knee.
"We are disappointed as he wants to make a big contribution. It will be Christmas, New Year time until we have him back available."
Sunderland had to play the first month without Wyke after he arrived at the club with knee ligament damage and was only a few games into his comeback when injury struck again.
Ross believes he has the squad to cope without the striker but admits his lengthy absence is a major blow.
Ross, on the early part of the season without Wyke, added: "I wouldn't say we just survived it, we did quite well. The group believe they can cope.
"Teams have got better at dealing with what we have got to offer, we have to mix it up a bit and cause them more problems.
"It is a blow."