Summer signing Gray, who stepped off the substitutes' bench to fire Barnsley's 88th-minute winner from the penalty spot at Blackpool on Saturday, is struggling with a slight groin strain.
But manager Mark Robins will be boosted by the return of midfielder Nathan Doyle, on loan from Hull, who missed the 2-1 weekend win through suspension.
Robins has no other new injury or suspension problems and apart from Gray has a fully-fit squad to choose from at Oakwell.
Gray, Jamal Campbell-Ryce and Iain Hume appeared as second-half substitutes on Saturday and Robins revealed they all staked their claims for a return to the starting line-up.
The Tykes are unbeaten in their last four league games and have won six out of their last eight to climb to within six points of a play-off spot.