Leeds United defender Gaetano Berardi is facing up to nine months out injured after suffering an ACL tear.
Berardi was stretchered off after half an hour during Sunday's 3-1 win against Derby at Pride Park.
The Switzerland international underwent scans on Monday which confirmed the injury.
A Leeds statement said: "Leeds United defender Gaetano Berardi suffered an ACL tear in his knee during Sunday's Sky Bet Championship fixture with Derby County.
"Berardi, who was replaced in the 33rdminute of the match at Pride Park, had scans today which confirmed the injury.
"The defender who has made 25 appearances for the Whites during the campaign, in which Leeds United won the Championship, now faces up to nine months on the sidelines."
Berardi's was not the only serious-looking injury of the match. Derby forward Tom Lawrence left the pitch with his arm in a sling just seven minutes in, having fallen awkwardly following a tackle by Berardi.