Steve Simonsen has returned to Stoke following the end of his loan spell so goalkeeper Kenny is in line to return to the side after completing a nine-month ban for failing a drugs test.
On-loan defender Paul Connolly has returned to Derby and, with no match fit full-backs at his disposal, Blackwell may play four centre-backs in defence.
Andy Taylor (ankle ligament damage) and Darius Henderson (hamstring) have been ruled out, while Jordan Stewart, Ryan France (both knee) and Jamie Ward (hamstring) remain sidelined.
Gary Naysmith and Derek Geary (both knee) are still not fully match fit as the injury crisis mounts at Bramall Lane.
Henri Camara (groin) and Ched Evans (broken collarbone) were on the bench for Sunday's 1-1 draw against Steel City rivals Sheffield Wednesday and should retain their places in the squad, although Evans is still lacking match fitness.