Julian Nagelsmann shuts down goalie talk after another Manuel Neuer error
Neuer was at fault for the opener, spilling a Christos Tzolis shot into the path of Georgios Masouras, who tapped home.
Arsenal forward Kai Havertz levelled the score early in the second-half and Brighton's Pascal Gross slammed in a winner in the final minute to turn the match around.
The post-game focus was however centred on Neuer, with Barcelona goalie Marc-Andre Ter Stegen watching on from the bench as he returned to his home stadium.
Nagelsmann already promised Neuer would be first choice for the tournament, which starts next Friday when Germany face Scotland in Munich.
Neuer made a late error in Monday's scoreless draw with Ukraine, and also made a crucial mistake for Bayern Munich in their Champions League semi-final loss to Real Madrid in May.
"I won't allow any discussions about Manuel Neuer, even if everyone's going to try.
"When he makes a mistake it's easy to say that it was his fault. But at the end of the day it was a series of mistakes.
"He pulled off three class saves during the match -- saves that others might not be able to make.
"Everything is fine."
At Barcelona for a decade, Ter Stegen is six years younger but has only played when Neuer has missed out through injury.
Earlier on Friday, Nagelsmann confirmed goalie Alexander Nuebel was cut from the squad, leaving Neuer, Ter Stegen and Hoffenheim's Oliver Baumann as the remaining 'keepers in the squad.
