Could see that ruining the deal if its a necessity on their part, such a clause being 'forced' by the player (even if slightly understandable) may not please the club.
Can't say i, personally, would let it stop us though. Not a better midfielder we are likely able to get this summer. Pretend like we wont want to give in to his demands, negotiate the clause a little to show you still have power, and then sign the **** out of him