The Irishman, 26, missed last weekend's FA Cup defeat to Aston Villa after sustaining the injury in training, but could be back in action at Coventry.
Blades manager Micky Adams said: "We want to get him assessed by a specialist and see how it settles down.
"He's had the problem before so he knows his own body and how long it could keep him out, but we've not ruled him out yet for Saturday.
"Since I've been here Mark has been a breath of fresh air. He looks on top of his game and as one of our senior players we could do with him in the current situation."