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You're right about City's Pep Guardiola play. Haaland and De Bruyne have helped a lot. Recently, Pep's plan has changed. City doesnt relie as much on these two players to score goals. The Champions League games versus Madrid and Bayern last year proved this was the appropriate strategy. There's a bug this season. De Bruyne, Bernardo Silva, Gundogan, and Mahrez's injuries and departures are difficult. Even if Bernardo Silva and John Stones are healthy, City may not be as good as before. City may be some people's best team, but the Champions League is coming up. Are Pep's younger players good enough?
If Bernardo Silva and Stones return to fitness, Pep could implement his usual 3-2-4-1 system. it's just that, there are several rotations that Pep Guardiola will do. for example, Haaland continues to fill his post as a lone striker. there are four supporting players behind him namely, Grealish, Kovacic, Alvarez and Silva. but the question is whether Kovacic is ready to play in his new position. I don't know for sure, but what is certain is that Pep often likes to rotate his players.
for the two pivots, it is still filled by its flagship players, namely Rodri and Stones. these two players really have good chemistry, they fill in the blanks left by each other. the rest, are defensive line players. or it could be Pep playing his young players, to fill in the position of attacking midfielder. this scenario, if De Bruyne remains injured. or it could also be that Pep will perfect the 4-2-3-1 system, depending on which player will become the main starter. but one thing for sure, Silva will still be a core player if he has fully recovered. As for other options that Pep can implement, it all depends on the condition of the players.
Well, referring to your question, suppose City no longer brings in newcomers at the end of the transfer window this summer. like it or not, Pep will rely on some of their young players such as Cole Palmer, Alvarez and Phil Foden. the rest, filled by Silva and Grealish as established players. maybe as you said, De Brunye's absence, Gundohan's departure, made City not as strong as last season. however, we must remember that Pep Guardiola's squad now has a winning mentality. they will do their job properly in this competition, and we will know their consistency once this competition starts.