Wow. If his lawyers didn't put it in writing that those increased wages were deferred wages, then he needs better lawyers.
Without knowing the intricacies around the deal, I speak here as an accountant. Any sort of clause converting the deferred wages into a “loan owed to FDJ” couldn’t work and it would defeat the intent of the restructure which was to “save wages in line with the La liga approved wage bill ratio to income” (something along those La liga lines.
From an accounting and legal standpoint, if such a clause existed whereby those wages were still owed to FDJ for, as an example, the 2020 and 2021 seasons, Barca would have needed to account for those wages - ie there would not have been a reduction in their wage bill.
Instead, they “deferred” it in such a manner that his earnings in year 1 and 2 were much less, only for his years 3-6 earnings being increased from his original base plus the “deferred earnings” from years 1 & 2. i.e. FDJ will actually only legally be due those wages over the next 4 years if his contract.
What Barca are doing by trying to sell him and not pay him those deferred wages is obviously against the spirit/intent of the agreement. FDJ (& others), helped them out when they were in a tough spot & now they’re trying to stab him in the back.
I know they owe Messi and Pique money as well but I’m not sure what those payments were for/or how they structured those agreements. Messi’s we’re loyalty bonuses or something, iirc.