At this point, I honestly believe that City should not care about UCL at all this season. It is not going to end up with them winning it, we can see that and know that, and going any further would give them just a smaller amount of money that they do not need, they are already a rich club. So, it would make more sense if they could just end up with a better return without having any of these issues.
I believe that we are going to see something great here, something that benefits everyone, and that will not be all that easy to recover if they focus on UCL too much. Ignore UCL, and focus on EPL and try to be in the top four at the end of the season, that is all they should be caring about at the moment.
The truth is that once Manchester City get their form back, it is possible they will focus on both the Champions League and their domestic league. However, if Guardiola notices that they are still in average form, he will definitely prefer to focus more on the Premier League so they can finish in a better position in the league table, ensuring Manchester City qualify for next season's Champions League.
At this moment, even if they focus solely on the Premier League, they are still likely to get bad results because they are not in good form. Let's just wait and see what happens in the January transfer window; maybe Guardiola will be able to sign a great player to replace Rodri.