Danny Wilson has revealed goalkeeper Mark Howard is battling to be fit before the end of the campaign.
The 26-year-old started the season as the Blades number one, but has been sidelined since suffering a thigh muscle at Leyton Orient in October.
He featured in a U21 game last month, but was withdrawn at half-time with an associated problem and Wilson concedes progress has been much slower than expected.
In light of Howard's continued absence, the Blades boss insists he would have no qualms about playing 39-year-old Danny Coyne if circumstances ruled George Long out of action.
The Gaffer, who also confirmed Lecsinel Jean-Francois, remains two weeks away from a return to full training, said:
"I am not too sure what will happen with Mark (Howard), this thigh problem has gone on a hell of a long time now.
"We expected him back well before now, but he keeps suffering with these minor setbacks and we aren't sure whether he will play again before the season finishes.
"Danny (Coyne) has been fantastic with George (Long) and a fantastic addition to the squad and dressing room.
"I would have no worries at all if we had to play Danny, he has played at the top level, even internationally, and he remains in great shape.
"Lecsinel (Jean-Francois) is like Mark in many respects, we think he is progressing well, then he suffers a setback."