De Bruyne is Man City's mainstay midfielder. This really had quite an effect on Man City. Moreover, based on information, De Bruyne's injury was quite severe, so he should probably be absent until the end of the year.
This is bad.
If he has to be absent for that long, Man City should seriously look for ways so that their performance is not much different when de Bruyne is around. Even though it certainly won't be the same, because after all, Man City will definitely lose one of its strengths, de Bruyne can be said to be quite difficult to replace.
I haven't heard about this but what I've read from some sources is that De Bruyne being out for 4 months is possible but I haven't heard if De Bruyne will be out until the end of the season.
But if it is true that his absence is longer then this will be a heavy blow to Manchester City even though there are still several players who can be maximised such as Foden and reportedly Manchester City are also looking for other alternatives, one of which is approaching Lucas Paqueta, but still this will provide a little gap. The hope now is that De Bruyne can recover in time and until then Manchester City must find the right alternative to replace De Bruyne in midfield and as the initiation of their attacks.