The 22-year-old was replaced at half time during Austria’s 1-1 draw with Bosnia-Herzegovina on Tuesday night, and tests performed back in Munich confirmed the club’s worst fears.
Alaba will need a seven-week break before being able to return to full training, effectively ruling him out until the very last weeks of the Bundesliga season, but the defender is determined to feature again this term.
“Of course I’m deeply sad,” Alaba said. “But I have a big goal in my eyes and I want to be back for the end of the season.
“I’m going to get a good rest now and then give it my all in rehabilitation.”
Alaba missed the end of the first half of the season due to a similar injury in his right knee last November.
He will now wear a plaster cast for two weeks before having a plate inserted in his knee, but should be able to start light training in four weeks’ time.
Alaba has featured for Pep Guardiola’s side 28 times this season, and made his 100th appearance for Bayern in their 2-0 defeat to Borussia Monchengladbach 10 days ago.
The Bundesliga leaders travel to Borussia Dortmund on Saturday as they look to maintain their 10-point gap at the top of the table.