The Belgian defender pulled up with a hamstring injury during the first half of our Champions League victory over Real Madrid on November 1 and missed the win over Crystal Palace just before the international break as a result.
Speaking ahead of Saturday's north London derby, manager Mauricio said: "We need to assess him. We expect (him to be out) longer than we previously (believed) when the problem happened. Maybe after Christmas, maybe. That is the expectation. It will be longer (than we thought).
"The injury is in his hamstring. He feels normal, he feels disappointed. It’s a little bit sad but in the same way he is focused now on trying to recover as soon as possible. He is working hard and he is in the first stage of his rehab.
"With this type of injury we must be cautious and it is a process of time."
Read our team news update ahead of our trip to the Emirates here.