Hosts Germany face being without both first choice centre backs in the last 16 match at Euro 2024 because Antonio Rüdiger has suffered a thigh strain.
The domestic federation DFB confirmed the nature of the injury on Monday.
Real Madrid's Rüdiger sustained the injury during Sunday's 1-1 draw against Switzerland, and it is unclear whether he will be fit again for Saturday's match in Dortmund.
His partner in the heart of the defence, Bayer Leverkusen's Jonathan Tah, will miss the match over a suspension after picking up a second yellow card against the Swiss.
Nico Schlotterbeck came on for Tah for the last half hour on Sunday, which could be an indication that he would also take his place in the last 16 match.
Waldemar Anton would be the candidate to replace Rüdiger should he not be fit to play, but coach Julian Nagelsmann also has a fifth centre back in Robin Koch.
Germany will play the runner-up from Group C, which is completed on Tuesday. All four teams are possible opponents: England, Denmark, Serbia and Slovenia.
Germany's starters all got a rest on Monday, with only the substitutes and reserves training at their base camp in Herzogeaurach, including striker Niclas Füllkrug, who scored a stoppage time equalizer against the Swiss.
All players then have Tuesday off before preparations for the first knock-out match start on Wednesday.
