The German said the 24-year-old's recovery was on track with what they expected but played down his chances of making the game against their top-four rivals.
"Unfortunately we don't have him back in (team) training. He makes his own training and that is the big difference," he added.
"We don't have him in full training so there is no reason to think about when he is back.
"We cannot rush the situation. We don't want to rush it. It was a serious injury and it is still so we need to wait.
"Whenever he is back the season is long enough that he can help us but we cannot rush it because there are a few games now.
"More or less he is on track. It is a lot about experience. He was in a very good way and then it was more difficult because of a reaction in the ankle and we had to cool down the situation a little bit.
"I don't think it will be long term but the game everyone is dreaming of is City: it was clear from the first second of the injury this would be extremely unlikely but it was the words of Phil so we will try to do it.
"At this moment it is not more likely than before but I don't want to say it is not possible."