I am sure PSG will see a huge increase in their revenue due to Messi. People said exactly the same last year here when discussing how City-CFG can afford him mentioning brand new sponsors coming in, existing sponsors paying more for Messi, the standard image right business that from his own lucrative commercial deals the club profits too and so on ...
Even if they ask their Qatar Tourism sponsor deal to put more money form one pocket to other to pay more to the club who could say its not fair when its about a Messi sized "increase". Messi will be the face of Qatar WC and that worth a lot of money for next 2 years and not just from Qatar related sponsors.
all this "omg how will PSg afford this adding so much salary to their wage bill" i think they will be fine without FFP issues. they kept the transfer fees really low, something like 60m GBP spent, that is 10m per year isnt it. absolute nothing.
Ramos, Donnarumma, Hakimi, Messi salary will add to the wage bill for sure, but I doubt Ramos, Hakimi gets much more if any than our players in similar position.
Donnarumma has maybe a big contract but he is maybe the best keeper for next 10 years overall the new Neuer maybe, I rate him highly and picked up for free gives them a chance to balance his salary out because otherwise he could have been a 100m priced keeper look at Allison, Kepa pricing from years ago.
PSG could raise ticket prices by 100% and they would sell out only from tourist going there to watch Messi imo. they will start selling all kind of merchandize and people will buy them even if they didnt care about PSG until the day Messi joins them. Messi is a seller, he sells on a way different level than any athelte in the world. its not like he sells more kit than KDB or Salah or similar players. he sells way much more. he has fans by the millions who will want a Messi shirt from PSG. he will bring lot of supporters to PSG.they might only follow them for 2 years, some will stick after that too for sure but in that short period I expect a hike in revenue for PSG.
especially as he gets added to Mbappe and Neymar who are no mugs either when it comes to commercial value let alone football pitch value.
At the same time I am sure Barca will feel on their incomes that he is not there anymore even if they get rid of his salary which was a large chunk of money wasnt it.