Borussia Dortmund coach Jurgen Klopp believes that next season will be the toughest his side has faced since he has been in charge.

Klopp has led Dortmund to two consecutive Bundesliga titles, but fears that the expectations have been raised so high that it will be tough for the club to meet them.

"The problem is that it is easy to improve when things were going badly for you, but now the bar has been raised extremely high for me and my team," Klopp told Bild.

"We have [won the Bundesliga] twice and there can be no probability or guarantee about succeeding for a third time."

Dortmund completed the league and cup double last season.