Sheffield United fear that on-loan winger Keith Treacy could miss the rest of the season through injury.
The Blackburn man, who joined the Blades on a six-month deal in the summer, sustained a knee problem during Saturday's defeat at Swansea.
Treacy, 21, has been sent for further tests, but Bramall Lane boss Kevin Blackwell has admitted the prognosis is already looking gloomy.
Blackwell told the club's official website: "It isn't looking too good and we'll have clarification after he has had a scan.
"If it turns out to be cruciate ligament damage he will be out long-term, in the region of six to nine months.
"He knew something was wrong straight away when he felt his knee lock and then go backwards."