Brian Laws faces an anxious wait to find out the full extent of Frank Simek's ankle injury.
The defender suffered a heavy fall during Saturday's 2-1 defeat to Crystal Palace and is due to undergo a scan to determine the full extent of the ligament damage.
The USA international has made 17 appearances for the Owls this season, and has seen the club recover from a disastrous start which saw them lose their first six games.
The club are still only three points clear of the Championship relegation zone though, so Laws can ill-afford to be without key players over the important Christmas period.
"It doesn't look good at all," Laws said.
"He fell awkwardly and we are all very concerned. It certainly didn't look clever.
"Frankie is one of the strongest players we have mentally and when that lad goes down rolling around on the floor we know something is wrong.
"So I will keep my fingers crossed that it's not too serious."