Gerard Houllier has today confirmed that the German international will miss at least a week of action.
Houllier said: "Didi won't be able to play at Villa and he won't be able to play in the derby either.
"He will be out for one or two weeks. We'll know more when we discover exactly what the problem is.
"He told me he felt something before the Sunderland game but he knew it wasn't the time to be leaving the ship. Unfortunately he has to do that now.
"We have the squad to cover though. That is why you need three or four defensive midfielders in your squad because they are very important in modern football."
