Manchester United manager Louis van Gaal says Marcos Rojo does not need surgery on his dislocated shoulder but will be out for around six weeks.
The defender, a £16m summer recruit from Sporting Lisbon, picked up the injury in last week's 1-0 defeat against Manchester City to add to United's problems at the back.
We have always a risk that it happens again. Conservatively, it can be less than six weeks. If we have to operate, 12 weeks.
Van Gaal is already without the suspended Chris Smalling while Phil Jones (shin) and Jonny Evans (ankle) are both sidelined through injury.
Speaking ahead of Saturday's home game against Crystal Palace van Gaal said: "We don't need to operate on Marcos, which is a relief. But with this injury it is very difficult that it shall not happen again. And that is the problem.
"We have always a risk that it happens again. Conservatively, it can be less than six weeks. If we have to operate, 12 weeks."
Michael Carrick, recalled this week to the England squad, could again figure as a makeshift centre back but van Gaal has not ruled out entering the transfer market in January for more permanent cover.
"It is clear that a lot of things happen and you can judge better in good times than you can in bad times," he said. "Maybe you are right (about buying in January) but we have to see about that."
And the Dutchman, who signed a three-year deal in the summer, claims it's not only in defence where he has injury problems ahead of the visit of Neil Warnock's side.
On-loan striker Radamel Falcao has missed the last two games after receiving a kick in training and he too looks set to sit out the match.
I feel very lousy for the fans firstly, but also for the board because they have a great belief in me and my players and my staff.
Falcao has scored just one goal since his deadline-day move from Monaco but van Gaal is refusing to get too downbeat on the Colombian's return in front of goal until he has regained full fitness.
"I cannot judge him now because now he is injured," van Gaal added.