"The France international sustained capsular ligament damage to his left ankle in training on Wednesday," read a statement on Bayern's official website (www.fcbayern.com).
"Coman will be sidelined for an indefinite period and is definitely out of the early matches of the new season."
Coman, who featured in France's Euro 2016 final defeat by Portugal last month, played 23 games in Bayern's Bundesliga-winning campaign last term, having won two French titles with Paris St-Germain and Serie A with Juventus in 2015.
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Bayern start at home to Werder Bremen on Aug. 26 and visit fourth-tier Jena in the German Cup first round on Friday.
(Reporting by Ed Dove; editing by Ken Ferris)
