Arsenal though have added some new players this season and formed an injury free squad but still I am not too optimistic about Arsenal especially in the Champions League. Manchester United can do well in the Premier League but they are unlikely to do well in the Champions League either. In this case, Manchester City will maintain their continuity from the English Premier League. Manchester City have done well this season and they will do well in the Champions League next season. With only one change, Manchester City's squad is unchanged and everyone is in top form, so expect Manchester City to be among the favorites for the Champions League next season.
Of course Manchester City is still the favorite because their current strength is very strong and Pep Guardiola has formed this team for the long term from the past and now is the result of their process, maybe for the next few seasons Manchester City will still be a strong team and in favorite at UCL.
But don't underestimate Arsenal either because this team has improved since last season and of course for next season there will be many changes made by Arteta to make this team even stronger, even though they are not the favorites but I'm sure Arsenal can pose a serious threat to the favorite team.
The thing is, nobody else got any much better, and that's their trouble. I mean if we were talking about how City is good but X team got so much better this season so they could rival, then I would understand another option but looking at the transfers no other team got any closer to City as well.
The only thing that could hurt them is complacency, because they already made the treble, and they could win the domestic super cup, and uefa super cup, and then could win fifa club world cup, and that means six, and Pep did that before with Barcelona and "may" yet still do that with City as well. When you win that much, it may start to look like you are about to end up being a bit different and going to end up with not caring about it as much. That's their only risk.