The BVB coach says the midfield pair are major doubts for the club's crucial Champions League clash with Olympique de Marseille on Wednesday
Son Heung-Min struck the only goal of the game at Signal Iduna Park after just 18 minutes of play, as BVB fell 10 points behind Bundesliga leader Bayern Munich, but the second-half withdrawal of two key players was arguably even more concerning, with Wednesday's must-win Champions League clash with Olympique de Marseille in mind.
"Today is Saturday and while miracles do happen, they just haven't happened for us recently," Klopp told reporters. "We are now waiting for the diagnosis before next Wednesday's game.
"This is not an easy phase for us. The injuries do not look good. Given that two of our players are injured, possibly gravely so, it will make our next few games tricky."
Turning his attention to the game itself, Klopp was not impressed with his side's performance against their second-placed opponent.
"If you want to beat Leverkusen, you have to be really good - and we were not," he stated. "Although we started well, they defended well and forced us to play long balls.
"We were too passive and lacked the final ball. We raised our game in the second half, but were not as good as we can be."