De Bruyne was carried off on a stretcher after suffering the injury late in the 3-1 League Cup second-leg win at The Etihad Stadium that secured City's place in the final.
As well as the cup final, he will miss both legs of City's Champions League last 16 tie against Dynamo Kiev and will be doubtful for the quarter-finals in April if they qualify.
"Of course, he is a bit sad that he will miss so many important games like the Capital One Cup Final and Champions League but Kevin would not be Kevin if he wasn’t already thinking about playing again for City," his agent Patrick De Koster told the Guardian earlier on Thursday.
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Asked about the European Championship finals in France in June and July, which Belgium qualified for as group winners, De Koster, who had said De Bruyne would be sidelined for at least six weeks, added: "You never know. I’m not going to discuss that at the moment."
De Bruyne has been a key player for City this season as they challenge for the Premier League title as well as in Europe.
City are second in the English league, three points behind leaders Leicester City.
Manager Manuel Pellegrini said on Wednesday he was optimistic De Bruyne would not miss the rest of the season.
(Reporting by Alan Baldwin; Additional reporting by Ken Ferris, editing by Toby Davis)
