According to Adam Schefter, Rey Maualuga is going to miss 3 to 4 weeks for his knee injury:
Bengals LB Rey Maualuga sprained his MCL and is expected to be sidelined 3-4 weeks.— Adam Schefter (@AdamSchefter) October 28, 2013
Maualuga has been playing some of the best football of his NFL career this season. It stinks the Bengals are going to miss his presence in the middle, but they could shuffle things around to create a band-aid over the situation. We can begin to guess what the Bengals will do with the void at the position, but for now we know there will be a void for sometime.
At least it is believed he will come back from this injury to help the Bengals with the last quarter of the season. It could have been much worse.