Kyle Walker returns to Manchester because he will not be able to continue playing for the national team due to injury. It is not yet known how serious the injury is, but for Guardiola it is another big problem, and again it is related to the team's defense. City have two very important games coming up against Arsenal and Real Madrid soon, Walker is definitely an indispensable defensive player right now.
The news is Kyle Walker has a hamstring injury but this cannot be confirmed now only rumors say he will miss a few matches, this is clearly Kyle Walker is needed by Pep Guardiola in two more important ahead, Pep Guardiola's anticipation is now there maybe? Or will field Josko Gvardiol as his replacement.
Although it is quite heavy to lose Walker but Manchester City's defense still has some that can be relied on so this will not be a problem for Pep Guardiola however he will change the scenario first with Arsenal then next with Real Madrid to place the right defense position.