The Germany international has sustained a thigh problem.
Grant said: “He was very good in pre-season until he got injured three days before the start.
“He was a major part of our team, but we have not had him until now. We know he is important and he will do things that are good for us.
“For the moment the doctors say four months before he’s back, so it will be around February, but we need to wait and see.”
