Nottingham Forest defenders Kelvin Wilson and Danny Collins are both facing up to three months on the sidelines.
Forest manager Billy Davies revealed the news following his side's 1-0 defeat to Blackpool at the City Ground on Saturday.
Wilson has been struggling with a back problem since the 2-2 home draw with Middlesbrough on September 17 when he was substituted in the ninth minute.
The 28-year-old returned as a second-half substitute in the 1-1 draw with Bournemouth on October 19 but has not featured since and will now undergo an operation.
Collins, 33, was replaced by Collins when he sustained ankle ligament damage against Bournemouth and he will also now be absent for around 12 weeks.