Leeds United manager Dennis Wise fears that Jonathon Douglas will not be able to feature in the busy Christmas schedule.
The Republic of Ireland international twisted his knee in Saturday's 1-1 draw at Walsall and is waiting for the results of a scan to determine the extent of the problem.
Wise said: "He caught his studs in the grass and twisted his knee. Fingers crossed it isn't as bad as we first thought.
"It'll be a big disappointment if we lose him - he is important to us and his overall work-rate is fantastic - but we'll wait and see what happens. He'll have a scan and be treated in the right way."