Manager John McGlynn declined to disclose the identity of a player who is struggling to be fit for the SPL match, but defender Andy Webster was doubtful with a knock for the encounter at Ross County, which was postponed.
Long-term injury victims Danny Grainger and Jamie Hamill (both knee) are out.
Hibernian defender Ryan McGivern is expected to be fit after training on Wednesday.
The on-loan Manchester City defender missed last Saturday's 1-0 win over SPL leaders Celtic due to a hamstring problem.
McGivern could replace Lewis Stevenson at left-back for the trip across the capital to Tynecastle.