Bayern Munich has confirmed Lucas Hernandez suffered ligament damage when he injured his ankle in the 3-2 Champions League win over Olympiacos.
Hernandez was forced from the field before the hour mark in Greece in a fresh blow to Bayern's thinning defensive stocks.
The left-sided France international faces "several weeks" out, sporting director Hasan Salihamidzic said on Tuesday, although the club has not confirmed an exact timescale.
The latest in a series of injury problems for 23-year-old Hernandez comes less than a week after first-choice centre-back Niklas Sule underwent surgery on a torn anterior cruciate ligament.
"[Hernandez] suffered a partial rupture of the inner ligament on the right ankle," Bayern announced.
"This resulted from an investigation by the medical department to club doctor Hans-Wilhelm Müller-Wohlfahrt."
Hernandez had only recently returned from a knee injury that saw him become the subject of a club-versus-country row when he was called up to France's squad for the Euro 2020 qualifying double-header against Iceland and Turkey despite Bayern's wishes for him to recover at the club.
There was better news for Bayern in regards to Javi Martinez and Serge Gnabry, though.
Spain midfielder Martinez was taken off at half-time against Olympiacos but Bayern said he "only suffered neurogenic muscle hardening".
Gnabry took a knock to the knee in the fixture, but both are to take part in reduced training in the next few days.