The Championship club have learned that captain Ethan Ampadu will be out until at least January.
Ampadu sustained a knee ligament injury in their win against Coventry City at the weekend.
"It's a serious knee injury, he has damaged his lateral ligament - the doctors have recommended a conservative treatment so he doesn't need surgery," Leeds boss Daniel Farke told BBC Radio Leeds.
"It's difficult to predict how long he will be out but it's realistic to speak about 10 weeks until he can return to team training.
"It could be a few days more or less depending on the rehab. At the moment we expect him to be back in training at some point in December but he will need a bit of team training before he's available.
"We expect him to be back (playing) at some point in January."