James Rodriguez faces several weeks on the sidelines after Bayern Munich announced the midfielder has a knee injury.
That loss left the champions seven points behind their rivals and news of James' injury deals a further blow to under-pressure head coach Niko Kovac.
Bayern confirmed on Wednesday that James has sustained a partial lateral collateral ligament tear in his left knee in training on Tuesday, an injury that will keep him out for several weeks.
"James' knee will initially be rested for 10 days before he begins treatment and rehabilitation," a club statement read.
James, 27, is therefore expected to miss the rest of 2018 and will not be able to play any further part in Bayern's Champions League group campaign.
Kovac, under fire after Bayern's slow start under his leadership, last month denied reports of a rift with James, who is on loan at the club from Real Madrid.
"We have a lot of international players. There will always be cases where one player plays and another doesn't," Kovac said. "James is a player of extraordinary quality and is important for the club. He's proved that several times, but I can't play with 12 men. He will play as many games as others."