Millwall midfielder Jimmy Abdou has had surgery to repair a dislocated collarbone and is expected to be unavailable until late December.
Abdou, 31, was injured during the recent defeat at Peterborough.
Lions midfielder Ed Upson suffered medial knee ligament damage in the same match and is likely to be out until at least the middle of next month.
Millwall manager Neil Harris recently said he was considering bringing in a loan signing as cover.
Forward Paris Cowan-Hall, who has been struggling with a groin injury, is expected to return to training in the next week.