Derby County midfielder Paul Green will be out for up to nine months with a knee ligament injury.
The 27-year-old was hurt during Saturday's loss at Cardiff and initial scans on Tuesday revealed damage to both the cruciate and medial ligaments.
Boss Nigel Clough told BBC Radio Derby: "The main thing is that nobody rushes him back. He's got five or six years left in his career."
Defender Gareth Roberts is likely to miss two matches with a knee injury.
Roberts, who also suffered a knee ligament injury in the game against the Bluebirds, will miss the matches with Coventry and Leeds.
Green must wait until the injury settles down before he has surgery.
The Republic of Ireland international joined the Rams in the summer of 2008 from Doncaster and has made 98 league appearances.