Derby captain Shaun Barker could be sidelined for up to 12 months after scans revealed the full extent of his knee injury.
The 29-year-old was stretchered off during the Rams' 1-0 victory over local rivals Nottingham Forest on 13th March.
It has now been revealed that he dislocated his kneecap and ruptured cruciate ligaments against the Reds.
The centre-half is scheduled to undergo surgery next week and Derby boss Nigel Clough has admitted that Barker could be missing for up to a year.
He said: "Without any question, this is a hammer blow for Shaun and we're all gutted for him that he's going to be out of action for quite some time.
"It's obviously hard for Shaun to take right now, but it's important for him to know we're all here for him and he will have the support of everyone at Derby County every step of the way.
"We have one of the best guys in the country, if not the best, operating on Shaun and he has said he will be able to make a full recovery and play at this level again.
"Twelve months is a long time but Shaun's strength of character and determination will see him bounce back."