The Dane was forced off in victory at Manchester City on Saturday.
Tuchel said, "He was injured some weeks ago with the same injury. I hope that it's not too bad and we get him back because he is so crucial.
Tuchel also praised the performance of Timo Werner, who had a goal disallowed.
He added: "In the last week he's really adapted well to the situations. The way he works he's relentless. He really wants it and I am very happy with his performance today."