The opportunity does exist for Manchester City to add another title in the Champions League this season, but it's still too early to talk about now because we haven't seen how all the teams that entered the Champions League will look like this season. There will definitely be surprises in the Champions League this season and all teams really have to work harder when competing in the Champions League because strong teams are not only in England, but also from other countries this season.
I've my nominations for clubs that exhibits good chances of lifting the trophy. However I will not disclosed that information yet, because we're yet to discover the performance from these competitive clubs, besides it's still early to decides the winner. When it comes to UEFA Champions League, I don’t expect these clubs to be reluctant in their performance, everyone wants the CL trophy which is up for grab from any elite competitive club. Like you said, Manchester City are the reigning champions, but I don't expect the cityzens to win two times in a row, it's impossible for an English club to do that, because it would be that Pep Guardiola wants to repeat history.