I may be completely wrong and naïve, but as others have said, I think the problems run deeper / higher than MM.

McCarthy, like Warnock, is an old school, wiley manager who has been around the block more than enough times. If he's not getting what he wants then, at a guess, I'd have thought he well knows how to show and share his dissatisfaction. I.e.. if you don't back me in the transfer market, this is what we end up with on the pitch. And thus he'll be quite happy to stick this out until they pay him off and sack him. Therefore it comes down to money...on and off the pitch.