The Blues left back, who scored the only goal of the game against Forest, picked up the knee injury at The City Ground and Steve Bruce told listeners to Tom Ross' Capital Gold radio show on Friday night that scans have shown that Clapham needs a cartilage operation which he will undergo on Monday.
Clapham missed a huge part of last season after firstly picking up a hamstring injury and then after he had recovered from that he picked up a dose of shingles.
Bruce estimated that Clapham will be sidelined for up to a month with this latest injury.