The return of Shinji Kagawa from Manchester United last Sunday meant the Bundesliga giants had to make a decision on who to leave out of their European party.
Ji, who arrived at Signal Iduna Park in the close-season, has yet to make an appearance for Dortmund, having been sidelined with a thigh injury sustained in training last month.
As such, Klopp has opted to leave the former Sunderland striker out of his Champions League squad, although he intends to review the situation should Dortmund make it out of the group stages.
"We had to make a decision," Klopp is quoted as saying by Bild.
"It's not like I thought 'yippee'. The decision with Ji was really tough for me. In the winter there will be a new decision [to make]."
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.