Manager Gary Johnson told the club's official website: "It's the lesser of the evils and it's not as bad as feared.
"It's likely Marvin will be unavailable for a couple of weeks. We have to let the swelling go down and the bone bruising before he can achieve full extension of the knee.
"We've had a torrid time with injuries and illness this season already, so the fact this news is better than originally feared should be seen as a positive."
Meanwhile, Evander Sno (back) and Jamie McAllister (calf) are still struggling with injury.