German Federation vice-president Ralph-Uwe Schaffert has taken aim at Barcelona midfielder Ilkay Gundogan.
Schaffert has accused Gundogan of consciously underperforming for Germany.
He told Hannoversche Allgemeine: "Ilkay Gndogan, for example, strangely plays outstandingly for the club and then plays in such a way for the national team that one can come to think: Has he sent his less talented twin brother?
"I don't understand it.
"I have many doubts regarding next year's Euro Cup. In terms of potential, we can go far. But aspirations, expectations and reality are so far apart at the moment that it is absolutely inexplicable to me. I don't think it's due to the coach.
"I get the feeling that quite a few of the players currently on the field believe they can go out on the field with maybe 85% of their potential commitment, and then you have to discover that that's no longer enough with this attitude.
"Maybe we no longer need only the very talented, but also those who are willing to roll up their sleeves. The best example of how to do this was given by our U-17s when they won the World Cup."