Paddy Kenny will make his first appearance of the season when Sheffield United host play-off hopefuls Swansea.
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.
Swansea duo Angel Rangel and Craig Beattie are back in contention for starting berths.
Defender Rangel sat out last weekend's 3-1 win over Barnsley with a groin injury and it was thought he may miss the rest of the season, but he has recovered well and could make his return at Bramall Lane.
Injury-prone striker Beattie has been out since April with a hip muscle problem but he has returned to training and could also be set to feature.
Alan Tate is doubtful as he continues to recover from the ankle injury which has caused him to miss the last few matches.
Ferrie Bodde (knee) and Jordi Lopez (ankle) remain long-term absentees for the Welsh side, who are bidding to secure a Championship play-off place.
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