The 23-year-old central midfielder has been out of action since August 2013, and although he has recently returned to training, Klopp refused to confirm whether he would play any part against Stuttgart tomorrow.
"The day Ilkay Gundogan will return to action will be a great day for everyone," Klopp told reporters.
"But 14 months on the sidelines are 14 months. We will stay calm, in spite of our injury problems."
Dortmund have won two and lost two of their opening four league games so far this season.