I don't know how many times I have stated this but UEFA cannot take any action against City based on criteria that contravenes European Law which City may decide to argue it does. UEFA works on an invitation basis but they need to have reasonable grounds to not invite a club and FFP, if illegal, would obviously constitute that. If FFP is agreed to be in line with EU law then fine, City & PSG must adhere to that criteria, regardless of the immorality of it which is an entirely different argument for another time. But the point that you are missing is FFP must be in line with EU law and if it isn't they cannot punish a club based on their failure to comply with it.
Its not a question of whether it breaches EU law per se. There are many occasions when that happens in life, the EU is vastly complex and doesn't have the same simple laws we use everyday. What matters is whether the objectives behind doing so are acceptable & the method is proportionate. A good example would be the way that fishing is restricted in the EU. Granted that has its own policy, but the principle is analogous - wrecking the fishing industry through rampant consumerism is bad, so it's restricted, even though fishermen lose out on trade.
So Dupont will be challenging FFP on the basis that it restricts trade between clubs and as such is preventing his client making as good a living as he otherwise could. In this case the grounds that UEFA will be claiming in response is that football across Europe is an essential part of the way of life for so many people (unarguable I think) and therefore it needs protecting.
The next stage is to prove that FFP will do this, that the way it does it is proportionate and that there isn't a way to achieve the same result by different, better, more fairer means. We can argue all night (and have) about whether this is the case. That fact alone tells us the issue isn't black and white.
Dupont's case is certainly interesting. The fact that there's a lawyer challenging the case doesn't mean much by itself. You want a lawyer to challenge something?
I can get you a lawyer by 3 o'clock. Since the
European Clubs Association (formerly the G14) has already agreed to abide by FFP, none of its members are able to mount a legal challenge. This is why City can't do a legal challenge themselves. As a result a third party is doing it.
Given the insane complexity of EU law its hard to say yay or nay to a successful claim with absolute conviction. However what we can say is this is unlike the Bosman case & the success of that shouldn't influence the success of this. In the Bosman case the basic point was that sports were found to be subject to EU law the same as every other industry. In this case its already accepted that sporting activity is subject to the same laws as the rest of us use. Instead its just about testing whether the implementation of newly introduced rules breach the very complex trade laws of the EU.
However its worth pointing out a few things. Firstly the case will run for years, particularly given the appeal/counter-appeal shenanigans that come with any case. And even if FFP is found to breach trade laws, as far as I understand it UEFA will still be given the opportunity to tweak it rather than ditch it. So its probably not something that will change City's summer transfer plans, for example. They'll have to continue assuming FFP is there for a while yet.
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