Louis van Gaal has revealed Wayne Rooney will miss Manchester United's games against West Ham and Wolfsburg with a "nasty" ankle injury.
The England captain sustained the injury last weekend in United's draw with Leicester and now Van Gaal has revealed it is much worse than originally feared.
Speaking at his weekly press conference, Van Gaal said: "Wayne's is a nasty injury. When we go on, it's been getting worse. We have to let him train to make the ankle stronger, that's very important.
"I cannot say [how long he'll be out] because the doctor shall decide that with Wayne of course. He is training well in the rehabilitation."
United travel to Germany to play Wolfsburg in a key Champions League game on Tuesday and must win to be sure of reaching the knockout stages.
When asked if Rooney was likely to miss that game, Van Gaal said: "Yes, I think so. His ankle is not good enough and we have to recover that ankle with a lot of strength. He has to do a lot of exercises to make it stronger."
I cannot say [how long he'll be out] because the doctor shall decide that with Wayne of course.
The Dutchman also confirmed defender Marcos Rojo will be sidelined for a number of weeks after dislocating his shoulder in training, joining Phil Jones, Luke Shaw, Ander Herrera and Antonio Valencia on the injury list.
"It was already in the media - Rojo has been injured," Van Gaal confirmed. "He dislocated his shoulder which is more or less the same thing that happened last season, meaning he is out for more weeks.
"The question as to whether he shall be operated is a question for the doctor and for Marcos.
"It's very unfortunate, also in the position of Luke Shaw so I have a great problem. [Jesse] Lingard is coming back which is good news. Jones is still injured so we have six injuries."
Rojo's injury leaves United without a recognised left-back and Van Gaal will have to rely on Daley Blind and Ashley Young to cover the position over the busy Christmas period, while Matteo Darmian and teenager Cameron Borthwick-Jackson are alternative options. Tyler Blackett is on loan at Celtic for the season.
Van Gaal stated in November that Shaw's long-term injury could prompt him to look for cover in the January transfer window and he admitted United's growing injury list now makes that more likely.
"They are always contact injuries and you cannot afford that," Van Gaal said. "We have a lot of contact injuries and also long-lasting injuries so that's our problem.
"So we are looking [at players for January] but as you know it is not so easy to buy players and in January it is more difficult. We are looking but it is not for sure."