Derby County defender Craig Forsyth has ruptured his anterior cruciate ligament (ACL) after missing the majority of last season with the same injury.
The 27-year-old picked up the injury in the Rams’ goalless draw against Aston Villa on Saturday.
He damaged his ACL in Derby’s 1-0 win against QPR in November 2015 and missed the rest of the 2015-16 campaign.
“He will have all the support he needs from the club in his rehabilitation,” boss Nigel Pearson said.
The left-back, who joined the club from Watford in 2013, was making just his fourth appearance for the club since returning from the injury.
He will now undergo surgery on his knee before beginning a rehabilitation programme.