Sheffield United midfielder Nick Montgomery is facing up to six weeks on the sidelines due to a knee injury.
Montgomery picked up the problem during Saturday's 1-1 draw with Millwall, although he was able to play the full 90 minutes at Bramall Lane.
However, he tore his cartilage and has also suffered possible damage to his ligament to put a dent in the Blades' bid to climb to Championship safety.
Blades boss Micky Adams said: "He has a cartilage tear and possible damage to his knee ligaments, so he'll see a specialist, but it looks as if we'll be without him for between four and six weeks.
"It's a massive blow for our hopes of climbing out of trouble because since I arrived he's been excellent and his leadership qualities are there for all to see."
Montgomery's absence for Tuesday's home date with Reading is softened by the return from suspension of Lee Williamson, while Johnny Ertl could play in central midfield.