Pulisic has not represented Chelsea since the opening day of the season, the 23-year-old's most recent issue a result of a heavy challenge while on international duty with the United States.
While the winger was thought to be closing in on an appearance in the first-team squad, Tuchel revealed at a press conference on Tuesday that he would remain unavailable for the foreseeable future.
Speaking to reporters, Tuchel said: "He got injured in the match with the USA with a tough foul, hurt his ankle. There is nothing to worry in that we are hiding details. I cannot give you them because I am not a doctor.
"He has some setbacks, some pain in his ankle that disturbs him. With his quick movements, he feels it and isn't free in the movement, the recovery is not happening."
Pulisic is the only Chelsea absentee ahead of their Champions League fixture with Malmo. body check tags ::