Jurgen Klopp is missing a number of key players due to knocks and the club captain says the mood among the players has been dampened.
The Bundesliga giants have started the season in good form, despite a series of knocks keeping Kehl, Ilkay Gundogan, Marco Reus, Marcel Schmelzer, Lukasz Piszczek, Sven Bender and Nuri Sahin sidelined.
"The atmosphere in the dressing room is not at its best at the moment," the former Germany international told Ruhr Nachrichten. "It's true that we have to get fit again before the difficult weeks ahead of us. Everyone is trying their hardest."
Kehl has missed a lot of soccer due to injury in recent years and the former Freiburg man is grateful for the faith the club has shown in him.
"When I was injured for a long time, they gave me a lot of time and made me confident," he said. "You don't forget those things."
Dortmund is set to enter a critical period of the season, with two Champions League games against Arsenal and Bundesliga showdowns with Hannover and Schalke on the horizon.