Made In Senegal charts Mane's rise from humble beginnings in Africa to becoming one of the best players in world football, which culminated with him winning the Champions League in Madrid last summer.
Speaking in the film, Klopp admits he wasn't particularly impressed with the first impression Mane gave.
The Liverpool boss said: "I remember my first encounter with Sadio. It was in Dortmund. There was a really young guy sitting there. His baseball cap was askew, the blond streak he still has today.
"He looked like a rapper just starting out. I thought, 'I don't have time for this'. Our team back then really wasn't bad. I needed someone who could handle not being a starter at the very beginning, someone I could develop.
"I'd say I have a pretty good feeling for people, but was I wrong! I followed his further career and continued success at Salzburg. In Southampton he just dominated."