Treacy had a scan yesterday (Monday) afternoon to see the full extent to his injury. Kevin Blackwell fears that the Irishman could be out for several months, but the club will make an announcement when the scan results return.
Kyel Reid will be hoping to deputise on the left-wing against a defence which are currently leaking in goals. The £3m Ched Evans had to settle for a place on the bench at Swansea - he is likely to start though. Glen Little is also another option on the wings, as is David Cotterill.
Gary Naysmith remains a long-term absentee.
Alex Bruce has been ruled out of the game, and Gareth McAuley, a rumoured Blades target, is in a race against time.