The 17-year-old defender was one of six Dallas players on trial at Bayern this month as part of a partnership agreement between the clubs and now joins on loan until the end of the 2020-21 season.
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Che, who said he was "honored" to stay with Bayern says the loan is all part of a learning experience for him.
"My goal is to one day be a professional player at the highest level, playing in one of the highest leagues. So, I'm very excited for this opportunity," he said in a video posted on the FC Dallas Twitter account.
Bayern said Che will be part of the under-19 team but will also have training opportunities with the reserve squad, which plays in Germany's third division.
The deal was possible before the age of 18, the usual minimum age for international transfers, because Che is also a German citizen, Bayern said.
Bayern signed defender Chris Richards from Dallas in 2019 after a similar loan spell. Richards has since played eight games for Bayern and made his debut for the U.S. national team in November.
"With Chris Richards, we have had excellent experiences with talent from our partner club. Justin is a young central defender with a lot of potential, as he recently showed in training. We are initially planning to have him in our U19 squad, but Justin will also have the opportunity to prove himself in training with the amateurs. We are very excited to see how Justin will develop over the next few months," Bayern academy director Jochen Sauer said in a team statement.
Information from the Associated Press was used in this report.