This is one of the things that will weaken Manchester City's performance against Real Madrid and Arsenal in the Premier League and in the UEFA Champions League, respectively. Kyle Walker is a good defender, and if he is not in the Manchester City squad that will face Real Madrid and Arsenal, the Manchester City defense will be vulnerable.
I totally agree with you because irrespective of how good Manchester City is and how they can easily cover up for a player who is injured but with the kind of player Kyle Walker is it will surely affect the performance of Manchester City because in terms of Manchester City defense Kyle Walker is there pillar and also no matter how strong a club is if there defense line is not good all there efforts will go to waste, although Kyle Walker injury is not that bad so he will surely play all there upcoming matches, so that's to say that Manchester City will be using all there full force on there upcoming matches.
I see that the performance of Manchester City players is quite even in all their lines and indeed they have proven that they do not experience a decline in performance when there is player rotation, the same goes for what will happen in the future, it is true that Kyle Walker is quite an influential player but that doesn't mean that if he is absent then the team's performance will decrease drastically.
Manchester City will face 2 difficult matches in the near future, against Arsenal and against Real Madrid and with the problems they are currently facing, many of their players are injured, even though it is difficult, I think Manchester City still has a big chance of getting through these difficult matches victory.
Definitely, Manchester city at this point can do without the presence of any notable player but sometimes the absence of a player that is always up and doing in most of their matches can cause some setback for the team more especially at the wing where such player represents and we all know the impact Kyle Walker presents in most of their matches as his personal ability to withstand some technical challenges within the defensive area cannot be overemphasized. Though Manchester city can still go without walker but it looks like a big blow because John stones is also ruled out as well.
Arsenal on the other hand looks somehow okay and prepared though the likes of Bukayo Saka may probably not feature due to a minor muscle injury he got in his hamstring that made him withdrew from England national team squad but however, there is every possibility that he would be present to face the match against City.
As for Real Madrid, they look more prepared for the champions league encounter with Manchester City but that not withstanding, it's a great game to watch between these two giants in the champions league quarter finals stage.