I don't think this is about legal action at all.Of course they are Petraccas. The question is what sort of legal action might they have against Melbourne FC?
Its a much lower hurdle ie. the AFL being satisfied that Melb acted with gross negligence and without Petracca's welfare paramount, in the events that transpired.
With the background of concussion, and law suits against the AFL, they would be hyper sensitive, and looking to be seen to be protecting Petracca and acting accordingly.
What may then transpire in terms of contract cancellation, trade facilitation (whether to a Club of his choice or otherwise), penalties on Melb, is completely unknown because we are in uncharted waters.