Murphy was forced out of last week's heavy defeat at Stevenage and is struggling with back and hamstring problems.
Teenager Callum McFadzean replaced Murphy and could be in line for his first league start for the Blades, but on-loan pair Jonathan Forte and Dominic Poleon provide manager Danny Wilson with further options.
Wilson has no other new injury or suspension worries, but could be tempted to make one or two changes.
Defender Danny Higginbotham and forward Chris Porter, back from his loan spell at Shrewsbury, are pushing for recalls.
Teenage striker Diego De Girolamo and defender Lecsinel Jean-Francois have both had surgery to repair cruciate ligament damage and will miss the rest of the season.
The Blades are hoping to climb back into an automatic promotion spot with victory over the second-placed Bees.