Midfielder Montgomery finished the 1-1 home draw with Millwall on Saturday, but tore his cartilage and is waiting to learn whether he has suffered ligament damage.
Adams said: "He has a cartilage tear and possible damage to his knee ligaments, so he'll see a specialist, but it looks as if we'll be without him for between four and six weeks.
"It's a massive blow for our hopes of climbing out of trouble because since I arrived he's been excellent and his leadership qualities are there for all to see."
Source: PA
Source: PA