Pep Guardiola must take advantage of the January transfer market if he wants to change or make his team rise and Manchester City management must also fully support it, otherwise I think their slump will be even deeper.
Pep Guardiola have been asked on few occasions of he'll be making some signings in the January transfer window so he can balance his team but his response have always been that he "wants his injured players back". Just like you said, the Spanish manager needs to make some significant additions to the team's so they can be competitive again but if he decides not to do that, I'll not be surprised to see Manchester City not finish the season in the top four.