Cologne stifled Dortmund throughout Saturday's Bundesliga clash at Signal Iduna Park, and even created the better chances with their pace on the break.
Klopp told Sky Sport: "Other teams have been struggling against Cologne.
"The very brightest moments were not there today, standards were okay, but overall too little. In the second half we were consistent and dynamic, but the lightness in the legs was gone."
Get the best features, fun and footballing frolics straight to your inbox every week.
Thank you for signing up to Four Four Two. You will receive a verification email shortly.
There was a problem. Please refresh the page and try again.