Bayern Munich sporting director Hasan Salihamidzic believes Lucas Hernandez will be sidelined for "several weeks" after suffering an ankle injury in Tuesday's Champions League victory.
Hernandez was forced from the field before the hour mark in Bayern's hard-fought 3-2 win away to Olympiacos as the team's defensive crisis worsened.
"He will be out for a long time. Several weeks," Salihamidzic told Sport1 following the match against Olympiacos.
On Hernandez, who was seen leaving the stadium on crutches, Bayern head coach Niko Kovac added: "Hernandez has problems with his ankle. We have to see whether the ligament was also affected.
"He has severe pain on the inside of his ankle; that's why we had to take him out. It's very frustrating."
Javi Martinez – who has been ravaged by injuries – was also substituted at half-time due to a muscle complaint.
"Martinez had a muscular problem in the first half, we didn't want to take any risks, so we reacted," Kovac said.
Bayern keeper Manuel Neuer was left frustrated by his side's performance, admitting more conviction is needed.
"The problem at the moment is that we need to score three goals every game to win because we keep conceding two," Neuer told UEFA.com.
"We made it difficult for ourselves again and didn't have enough conviction. We need to continue working on that, analysing and seeing what we can do better."