Schalke goalkeeper Ralf Fahrmann has undergone surgery on his left knee after suffering damage to the medial and anterior cruciate ligaments. With Fahrmann out for several months, coach Huub Stevens must decide whether to continue with youngster Lars Unnerstall or opt for former Germany keeper Timo Hildebrand, who has signed a contract until the end of the season. Stevens told the club\'s website: \"The surgery went well. It was important. If we hadn\'t treated the injury aggressively, it\'s likely that he\'d have problems with that knee again in two or three months.\" Hildebrand is set to make his debut for the club in a youth-team match against Standard Liege tomorrow.