Delap, on loan from Stoke, missed Saturday's home defeat to Bolton after sustaining a calf strain in training on Friday, while McNulty has an ankle injury.
Manager David Flitcroft, who employed striker Kelvin Etuhu as a right wing-back and midfielder Tomasz Cywka as a left wing-back against Bolton, could make further changes.
Flitcroft has no new injury or suspension problems, but midfielder Jacob Mellis and defender Stephen Foster are among those pushing for recalls.
Strikers Jason Scotland and Marlon Harewood may both have to settle for a place on the substitutes' bench again with recent loan signing Chris O'Grady expected to resume alongside Chris Dagnall.
The Tykes are looking to bounce back from successive defeats in their bid to stay out of the relegation zone.