The defender limped off in yesterday's 1-0 win at Sunderland with a recurrence of the calf injury which had sidelined him for the previous five games.
Lambert said: "It's the same as before. Hopefully it's not too bad, but I haven't really spoken to him. The Cup is not my priority and the Arsenal game is the most important one.
"I don't know if we have lost him. We'll have Ciaran (Clark) back for the Cup game and we'll see how it goes.
"Janoi (Donacien) was on the bench and he is straight from the academy. That shows you the lack of strength we've got and sometimes it's a needs must situation."