Bayern Munich have confirmed that defender 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 have 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.
His latest set-back leaves the Bundesliga champions with just Jerome Boateng as their only out-and-out fit centre-back, though the likes of Benjamin Pavard, David Alaba and Javi Martinez have experience of playing that position across their careers.
There was better news for Bayern in regards to Martinez and Serge Gnabry in the aftermath of their victory in Greece.
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.
Niko Kovac's side return to action on Saturday as they host newly-promoted Union Berlin looking for a first Bundesliga win in three matches.
Former Eintracht Frankfurt boss Kovac has again come under scrutiny following a defeat to Hoffeinheim and draw with Augsburg either side of the international break, with those results leaving the Bavarians sat third in the table.