Germany head coach Joachim Loew on Friday fired back at criticism from Sandro Wagner, who retired from international duty in mid-week after being left out of the extended World Cup squad.

"I took it as a criticism of his fellow players and he portrays some, who have played for us for an eternity and are senior players, as if they were complete idiots," said Loew at an event in Berlin on Friday.

"He makes out that they are only with us (in the national squad) because they don't speak their minds.

"He says that others don't open their mouths. What should the likes of Jerome (Boateng) and Mats (Hummels) think? It's completely outrageous."

The out-spoken Wagner, who scored five goals as Germany qualified for Russia 2018 with a perfect record of ten wins, resigned from international duty in protest after being left out of the 27-man extended squad on Tuesday.

"For me, it is clear that I do not seem to fit with the coaching team in the way I am always open, honest and address things directly," fumed Wagner, who has made eight appearances for Germany.

The burly forward, who is Robert Lewandowski's back-up at Bayern, was furious as Loew opted to include RB Leipzig's Timo Werner, Mario Gomez of VfB Stuttgart and Freiburg's Nils Petersen as his strikers.

Wagner indirectly accused the German squad of being packed with "yes men", a notion Loew rejects.

"I can understand a little bit that he is disappointed, that's clear," said Germany's World Cup-winning coach.

"But I find his reaction a bit over the top.

"Everyone who knows us knows how we always encourage players to voice their opinions, to be open and honest, to be critical of ourselves.

"These things are very important to us."

Germany open their World Cup campaign against Mexico in Moscow on June 17 and also face South Korea and Sweden in Group F.