Lecsinel Jean-Francois looks set for another spell on the sidelines after damaging his knee in the Johnstone Paint Trophy tie at Notts County.
Boss Danny Wilson revealed the blow ahead of Tuesday's clash with Walsall at Bramall Lane.
Confirming the problem, which is on Jean-Francois's other knee to the one he damaged in March, the Gaffer explained: "It is bad news for Lecs, he has tweaked his cartilage and looks set to miss around two months.
"We are gutted for him because he will have to have another operation to clear his knee out. It was such an innocuous collision and now he is back on the sidelines.
"The lad was champing at the bit to play, but that is football and he will come back a stronger and better player."