Julian Nagelsmann says he feels "incredibly sorry" for Lennart Karl after the teenager was ruled out of the World Cup through injury.
Germany face the United States in their final friendly ahead of the tournament, and Karl suffered an injury in their training session on Friday.
Nagelsmann said the 18-year-old had been rushed to hospital in his pre-match press conference, and Germany later announced he had torn a muscle in his thigh.
"I feel incredibly sorry for Lenny," Nagelsmann said. "With his carefree attitude, his flair for the game, his pace, and his personality, he was a perfect fit for the team.
"It's a huge shock for him and all of us that he's missing the World Cup. It's only a small consolation that he's young and has many tournaments ahead of him.
"We would have loved to have him on the team."
In a social media post, Karl added: "I don't even know where to start, but it hurts indescribably to have to miss the biggest tournament.
"Did everything to be fit for the World Cup. Unfortunately, injuries often come at the most unfortunate moment. I wish my team maximum success and, of course, I support them every minute!"
Karl, who has three Germany caps to his name, had impressed in their last friendly against Finland, getting an assist for their second goal in the 4-0 win.
RB Leipzig's Assan Ouedraogo has been called up in his place, having made his debut in Germany's 6-0 win over Slovakia in World Cup qualifying in November, scoring the final goal.
"With Assan Ouedraogo, we're now getting a player who, like Lenny, had a fantastic start with us," Nagelsmann added of their new addition.
"He's also highly talented, and we expect him to play with courage and freedom."
Ouedraogo will link up with Germany before their World Cup opener, in which they face Curacao on June 14.