Joshua Kimmich has questioned Germany's mentality after its shock 1-0 defeat to Mexico on Sunday.
The reigning champion was second best to El Tri throughout and was duly punished by Hirving Lozano's superb goal midway through the first half.
Germany had won just one of its six pre-World Cup friendlies after qualifying with a 100 per cent record and Kimmich believes a lack of intensity in those games contributed to the lacklustre performance against the Central Americans.
He said: "The mentality when facing a match of this level also counts, quality is not enough. We lacked that too, so many mistakes were made.
"Removing Saudi Arabia we have not won the last six games. You cannot compare the friendlies, in which the opponent does not press you as much as a qualifying round or a World Cup.
"The coach [Joachim Low] is right when he said that we lost a lot of balls. Mexico did well on the counter-attack, especially - they caught us several times."
Germany will be hoping to get its campaign back on track when it faces Sweden at the Fisht Stadium in Sochi on Saturday.