The Blades have lost their last five league matches, but turned in an impressive display last week at Wolves, particularly in the first half, and Weir has no new injury or suspension problems.
Winger Jamie Murphy could be added to the squad after missing the last five matches due to a groin problem, but midfielder Callum McFadzean (ankle) remains sidelined and misses the chance to play against his brother, Crawley defender Kyle.
Striker Shaun Miller, sidelined since damaging cruciate knee ligaments on Boxing Day last year, is edging closer to a return to action after playing 45 minutes of a behind-closed-doors friendly this week.
Gary Alexander returns to the Crawley squad for the trip to Sheffield United.
The veteran striker has completed a three-match ban after he was sent off against Gillingham last month.