De Bruyne is a key player obviusly but i think Manchester City can sub him very well, in fact i really think this injury helped Manchester City thinking in the future of the team. Now they know they can play very good without him, so we can some news in the next summer transfers window.
Manchester City was not competitive due to the absence of key players, until they appointed Pep Guardiola in 2016/2017 EPL campaign, Pep is widely recognized as aggressive coach that has full ambition for the team to become great. He doesn't lack the full tendency but always curious about the performance of his team, ensuring for placing alternatives options in situations were the intended primary ones failed. Kelvin De Bruyne is injured and has not been with Manchester City for months now, probably might return in January because he's gradually making some vital recoveries, most football lovers can't wait for Kelvin De Bruyne to start games on the pitch for the Citizens.
There can be no doubt, one of the reasons for Manchester City success in recent years is the influence of Guardiola who is able to manage the team well. Guardiola experience in managing big teams and his ingenuity in formulating strategies have made Manchester City successful in winning its first UCL trophy. This season, Guardiola has had a few problems in managing Manchester City due to the absence of key players who have contributed greatly to the team. Guardiola as manager certainly really wants the players who have been his mainstay to remain fit, but player injuries can come at any time.
Guardiola must be able to maintain Manchester City's quality at a high level even without the presence of several core players. Manchester City still has several other top players in the midfield position, Guardiola can rely on them even without Kevin De Bruyne. However, the quality of Kevin De Bruyne play has helped the team a lot so far, Guardiola really misses his presence back in the Manchester City squad.