Thomas Muller has said Germany "misjudged the situation" by believing that they would click into gear ahead of the 1-0 loss to Mexico.
The World Cup holders had won only one of six matches ahead of the tournament, but remained confident that they would be ready for the biggest stage.
But Germany looked flat as Mexico triumphed and Muller told reporters: "Fundamentally, it maybe was a bit reckless to think that after those friendlies, albeit addressing the mistakes and working on them, we'd be there with a certain freshness and play to our usual strengths once the tournament started.
"In hindsight, we definitely misjudged the situation."
Several reports in Germany have alleged rifts within the camp,but Muller said that was not true.
"There are no groups as was the case [at the European Championship] in 2012 when Bayern and Dortmund began competing with each other. The team chemistry at that time was not the best, but that's not the case now. There is nothing."
Germany general manager Oliver Bierhoff also dismissed the reports, saying: "I can only deny that.
"We had a bad start, also performance-wise, and now everyone's looking for a reason. But I don't see any conflicts within the squad. I don't see any problem there."
If results go against Germany on Saturday, their dream of becoming the first team to defend the title since Brazil in 1962 could be over and leave them as the third consecutive title holder to not to emerge from the group stages.
But asked what that scenario could would mean for the Germany coaching regime, which has been in place since 2004, Bierhoff said: "You always have to analyse a tournament and what needs changing. We've done it in the past, and we'll do it again.
"But nobody can take away from us what we achieved in 14 years. Not a single match. It would be a failure, but it wouldn't change what we've achieved."