Karl was injured during a training session on Friday, ahead of Saturday's practice against the USA. It is now clear that the muscle injury will cause the 18-year-old to miss the entire World Cup.
"It is a huge shock for him and all of us that he will miss the World Cup," said national team captain Julian Nagelsmann in a press release from the German Football Association.
The injury is a major blow to the German national team. Despite his young age, Karl scored nine goals and provided eight assists in 40 appearances for Bayern Munich last season.
Karl has been replaced by RB Leipzig's Assan Ouédraogo.
In the World Cup group stage, Germany will face Curaçao, Ivory Coast and Ecuador.
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