Bayern Munich said Tuesday defender Matthijs de Ligt would be out after suffering a knee injury at the club's training camp in Portugal.
The club did not specify how long the Dutch centre-back would spend on the sidelines but said in a statement that De Ligt would "not be able to train for now".
De Ligt suffered "a capsular injury in his left knee during the training camp in Faro, Portugal", Bayern said, with the diagnosis confirmed on site.
The absence of De Ligt could mean a baptism of fire for new recruit Eric Dier, who was signed to shore up Bayern's defence during the current January transfer window.
England international Dier followed in the footsteps of teammate Harry Kane in making the switch from Tottenham Hotspur to Bayern.
The German champions were already in need of reinforcements at the back with Kim Min-jae set to miss several games as he represents South Korea at the Asian Cup.
Bayern's next game is against Werder Bremen in Munich on Sunday. Thomas Tuchel's side sit second in the table, four points behind Bayer Leverkusen.