Derby are waiting to discover the extent of the knee injury suffered by skipper Shaun Barker against Nottingham Forest.
The defender left the game following lengthy medical attention after an innocuous-looking second-half collision when making a defensive clearance.
"We are all gutted for Shaun and his injury has taken the gloss off the victory somewhat because he is such an influential figure for us both in the dressing room and on the pitch," manager Nigel Clough said.
The 29-year-old was taken to hospital after being examined by Rams physio Neil Sullivan, who believes Barker has dislocated the patella in his right knee.
Barker missed the beginning of this season after undergoing knee surgery towards the end of the last campaign.
However, he has recently become a regular in the side and has made 22 appearances since making his comeback in November.