Not sure why everyone is focusing on whether Messi wants to leave the real issue isn't City or Messi but Barca.
Barca have an asset who will depreciate 150m euros over the next 4 years and who will cost them around 80m not that time. It is an asset that is actually worth less to them than to anyone else and an asset they have two replacements for and have shown they can be nearly as good without. Barca have debt and a new stadium to build and they can to choose to cash in and benefit from about 250m p and l boost or they can choose to keep and be marginally better than they would otherwise be ie they are probably the best attacking team in the world even without Messi.
So for me it is not about Messi but about Barca, he will soon get the message if they would prefer the cash and I can't see him staying if he is not their main priority and focus. It is this that will make the move happen and not Messi agitating. The trouble stopping the move is Barca want to come out of this the reluctant sellers so they can pretend they wanted to keep him in front of the fans whilst cashing in. This political game between club and player is huge at the moment.
The Real Madrid game clinched it for me 4-0 win without Messi . My bet is they won't keep both Messi and Neymar and they will cash in on the older one