I don't see the problem with a business owner using the expertise of one business he owns to facilitate a deal with a another project he's the chairman of. It sounds like an administrative task that was passed on('can you write me up a contract for this when you get time'). If they are suggesting this 'proves' the deal was a sham or that this somehow proves City are state owned(since the state do own Al Jazira Club), then that is another logical fallacy('anecdotal fallacy'?).
Unless of course, there are some regulations(UEFA, PL) we are not aware of, which would prevent this(which I doubt).