The Republic of Ireland international was stretchered off towards the end of the Lions' 1-0 victory at Bradford City on Saturday.
Reid was injured via a tackle from behind and The Lions are awaiting the outcome of tests to determine the extent of the problem.
The 22-year-old missed the opening three months of the campaign through injury and Lions manager Mark McGhee admits the outlook is bleak.
"It looks very much as if Reidy has damaged his medial knee ligaments," said McGhee.
"If that turns out to be the case he won't play again this season."
