The world champions have returned to the scene of their 2017 Confederations Cup triumph amid sweltering conditions in Sochi but are facing the heat on and off the pitch ahead of Saturday's crucial showdown with Sweden.
A 1-0 defeat to Mexico has put Germany under pressure and sparked reports of cliques in the team following the country's underwhelming Group F opener.
The topic of disharmony was inevitably raised during Wednesday's news conference after training and Muller dismissed the claims.
"Is that confirmed? Do you have a source? No? Ok," Muller said when asked if there were factions within the team amid a strong Bayern Munich presence.
"In 2012 we didn't have great chemistry, but that's not the case now."
Attempting to pinpoint what went wrong against the Mexicans, Muller highlighted Germany's performances in the lead-up to the World Cup, which saw Joachim Low's men scrape past Saudi Arabia having lost to Austria.
"I think we took things a bit too lightly after the warm-up games," Muller said. "Internally we made no bones about it, we were self-critical and said we need to do this, that and the other.
"And in warm-up games we had just hoped that in a non-training camp context, without tough and lengthy training sessions, we hoped that when the World Cup came around we could raise our game. And we haven't been able to. We need to get back to being prepared to walk that extra mile. That's it.
"What is important now is that we look ahead to the two major tasks lying ahead of us in this group. The heat is on."
Muller spoke after Bierhoff fronted the media at Germany's hotel amid questions over team unity.
Responding to the reports, Bierhoff told reporters: "I can say that the speech did not become as loud as it would have in earlier years. It is another generation and we live in other times. But the speech was very fair and square.
"It is important that we find - in terms of the atmosphere within the team and work - a good mixture between focus and tenseness in the next few days. The tenseness is there for sure. Everybody is aware that the match against Sweden is the first final for us. You know that these knockout matches are part of every tournament."