
He will undergo further treatment at Bayer 04. A replacement has yet to be called up.
Germany U21 coach Stefan Kuntz said: "It's a purely precautionary measure. In discussion with Jona, our doctors and Bayer Leverkusen we have reached the decision to send the player home for treatment. Of course, it's a pity one of our leading players misses out on the start of the European Championship qualifiers but we do have options in central defence in our squad."

Werkself-TV shows the highlights of the Bayer 04 women's 3-1 win at RB Leipzig on the 25th matchday of the Google Pixel Frauen-Bundesliga 2025/26.
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The Werkself need a win in their penultimate match of the season at RB Leipzig on Monday evening (18:00 CEST) to keep their hopes of third place alive until the final day. After Eintracht Frankfurt lost on Saturday, Roberto Pätzold's side can close the gap on their rivals to two points and leave it all to play for next Sunday.
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Werkself TV shows the highlights of Bayer 04's 1-3 loss at VfB Stuttgart on Matchday 33 of the 2025/26 Bundesliga season...
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Down to fifth from fourth place despite taking an early lead: in the head-to-head for a Champions League spot, Bayer 04 were 1-0 up at VfB Stuttgart with just a minute played thanks to an Aleix Garcia strike, but ultimately lost 3-1 (2-1) to the more determined hosts. It meant the Swabians leapfrogged the Werkself in the Bundesliga table on the penultimate matchday.
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