Lewis Macleod is struggling with a hamstring problem.
The midfielder did not make the Brentford squad for the home defeat against Swansea, having scored a late equaliser at West Brom last week.
The former Glasgow Rangers man, who recently rejected the offer of new contract, has been plagued by injury problems during his time at Griffin Park.
Bees head coach Thomas Frank confirmed: “He has a hamstring problem and we don’t know how long he will be out.”