Star midfielder Sander Berge, until recently the club's record signing, lasted only a few minutes of tonight's Bramall Lane clash with Manchester United before appearing to damage his hamstring.
Berge pulled up as he chased a ball down the right wing and went down instantly, before receiving some treatment from physio Paul Watson.
The Norwegian international was then replaced by Phil Jagielka and will be further assessed by United's medical staff, but if the injury is as bad as first feared he could miss a significant chunk of games over a busy festive period.