The absence of Rodri, Stones, and Diaz from the squad of Manchester City is affecting the formation of the team because it's just like the center-back and defensive midfielder of Manchester City which the three mentioned players occupy is empty, no right player of Manchester City has been up to fill in the vacuum in the team, which the three injured players have occupied for so long, which is now affecting the team formation from gaining three points easily in Manchester City matches in Premier League and Champions League.
They lost these players by injuries and they can think it's very unlucky but they can not blame it all on luck factor. They have a lot of money spent for player transfers and they must have better ability to avoid player injury crisis than other clubs. When things are good, people say Manchester City can win Premier League with two different squads but now they are struggling when not all one squad were injured. It's different from theory to reality and Manchester City will have to move on and keep fighting with competitors with not a best squad.
However, I am sure if Stones and Diaz can return to pitch by December, I am sure they will fill in the gap of Rodri, who will stay out of the season because of injury. By then, Manchester City's defense line will be strong, and not easily broken by their opponent.
You can follow up their injuries and recoveries with
https://www.sportsgambler.com/injuries/football/england-premier-league/But it is still Manchester City and I think it is quite usual that you can't fill one to one a gap that one of the best players in the world leaves behind due to times of being injured, but Manchester City can still replace players at a very high level. It is not like they are sending an amateur to fill the gap. They are still high profile players, but maybe not as good as the primary choice, but this is more or less standard for any team. You can never have two equally good world stars for the same position because they wouldn't accept to be sitting on the bench. Manchester City should be able to compensate for the loss in quality regardless and still remain sufficiently competitive to take on the challenge they are facing now.