Derby County boss Nigel Pearson has described the ACL injury sustained by Craig Forsyth as "incredibly unfortunate" after the defender suffered his second serious knee injury in nine months.
After working his way back to full fitness, Forsyth had featured in three of Derby's opening four games in the Championship but he faces another lengthy spell on the sidelines after rupturing his ACL against Aston Villa on Saturday.
Pearson told the club's official website: "This is incredibly unfortunate and disappointing news for Craig. He worked incredibly hard to get back to fitness for the start of pre-season training and had done well in the early-season games.
"He will have all the support and encouragement that he needs from everyone at the club during his rehabilitation work.
"He is a tremendous character and a popular member of the squad. We're certainly not putting a timeframe on when he will be back, but what is of paramount importance is that he returns once again to be an important member of our squad."
Forsyth has been with the East Midlands outfit since joining from Watford in 2013.
