Mario Gomez called Germany "stupid" for losing to England, and suggested his side let off the gas after going up 2-0 in their Berlin friendly on Saturday.
The Besiktas striker on loan from Fiorentina scored Germany's second to give the hosts a commanding lead on 57 minutes. However strikes from Harry Kane, Jamie Vardy and Eric Dier gave England a famous 3-2 victory.
Speaking to the DFB's official website, Gomez lamented Germany's foolish late display.
"I think that we set ourselves up in the right way but in spite of that, it is perhaps natural to take your foot off the gas when you are 2-0 up in a friendly," Gomez said.
"It's just how it is. We gave England a lot of room and they are blessed with a lot of individual quality. We were stupid to have lost this game.
"We lost our way and left too much space, which England used well. They scored two goals from set plays. We knew they would be dangerous from those situations and they showed that."
Germany next host Italy in Munich in another friendly on Tuesday. Gomez has targeted increased focus against the visiting Azzurri,
Gomez said: "We weren't good in the last 30 minutes and we need to look at that. We have to remain focused over the full 90 minutes, even if we are 2-0 up.
"We can't let it happen again as teams like England can take full advantage. In a major tournament, that results in you going home. That much is clear to us.
"Italy will obviously be a tough game as they have a good team and traditionally play very well against Germany. I think it's important to play well and get a good result to begin our preparations for the summer in a positive way."