"The muscle has been stitched up and the surgeons have cleaned up the wound thoroughly," club physio Dave Williams told the club's official website.
"There is no damage to the ligaments, but the recovery period just for the muscle to heal up is three weeks, with no stress to the area at all.
"That means three weeks on crutches for Hermann before he can even begin to build up the muscle.
"You are looking at probably six weeks at the minimum really before he could be back in action."