The only thing that will stop that is if our players start to look down their noses at Madrid.
Which I think has already happened with De Gea. I reckon he's disgusted with them procrastinating and fecking up the deal by going in at the very last second. They showed him no respect. Which is why there's been no rumblings coming out of De Gea's camp since.
De Gea still wants to go to Madrid. Its' only the fact that Navas is still soldiering on and Zidane is not one who makes excessive buys when he has sufficient tools to work with, that has prevented him from clamoring for a move. That, and the fact that Mourinho won 2 trophies and has steered us to the CL, which means he is happy to bide his time until Madrid come for him (Navas leaves/Zidane sacked, or whatever).
He's being tactical and pragmatic. Always remains non-committal in his interviews, not ruling out a move to Madrid, but at the same time stating his happiness to be a United player.
Regarding Morata, I would be happy if he didn't sign for a PL rival. I actually think he would become dangerous in Conte's system, and his link-up with Hazard would be terrific. So, better he goes to Milan.