Bayern Munich left-back David Alaba suffered a knee ligament injury during his side's 2-0 win over Roma in the Champions League on Wednesday.
Alaba put in a star performance for Bayern, setting up the opening goal with a pass to Franck Ribery. But he limped off with 10 minutes remaining.
Bayern's official Twitter account said he injured his MCL, with more tests to come.
.@David_Alaba picked up a medial collateral ligament injury in the match. There will be further tests in the morning. Get well soon!
- FC Bayern English (@FCBayernEN) November 5, 2014
Bayern manager Pep Guardiola said the Austrian international may have played his last football of 2014.
"With David Alaba we lose a great lad and a great player," Guardiola said. "He can play nearly every position on the field. He is very important for us. We just hope he will come back as soon as possible, but I think we will see him just after Christmas."
Bayern's injury list has swelled to include Alaba, Bastian Schweinsteiger, Holger Badstuber, Javi Martinez, Thiago Alcantara and Claudio Pizarro.