Javi Martinez is set to be absent until February after suffering a "bad muscular injury" in Bayern Munich's 2-0 win over Wolfsburg on Saturday.
Bayern ultimately ended 2019 with a crucial win as late goals from substitute Joshua Zirkzee, who has now come off the bench to score in each of his first two Bundesliga appearances, and Serge Gnabry broke Wolfsburg's resistance at the Allianz Arena.
However, the reigning champions' success was marred by another injury blow, with Martinez forced to limp off clutching his thigh at the end of the first half.
Interim head coach Hansi Flick said: "He will be out for a while. He suffered a bad muscular injury and will be sidelined for six weeks."
Bayern sit four points off the pace at the top of the table and resume their Bundesliga campaign against Hertha Berlin on January 19.
Flick was already facing a shortage of bodies prior to the Wolfsburg game, with Thiago Alcantara suspended and a host of first-team players injured.
Yet Zirkzee again seized a brief opportunity to make an impact, the teenager scoring just two minutes and 28 seconds after he had replaced Philippe Coutinho.
"I'm just proud of the team," said Flick. "We believed in the victory until the very end.
"It makes me proud to see the team coming together and showing that on the pitch."