If he wants to leave then just hand in a transfer request. It annoys me sometimes how revered Ronaldo is after he left for Madrid, and that's with him signing a contract just before he left so we'd at least get a huge amount for him.
De Gea not signing a contract, yet clearly wanting to leave for Madrid and not handing in a request annoys me more. He'll leave and some of us will go, "Oh good luck Dave, you gave us 4 solid years, he's going home blabla," forgetting he basically let his contract run down to force the club's hands. He'll get plaudits for being a supposed "class act" while he goes to Madrid, further establishing us as inferior mugs to those lot.
No doubt we'll hear about how he "enjoyed his time with United" or "how it was a magical 4 years" blabla, probably through some cheesy open letter to fans or something silly.
I swear United's loyalty to players hurts us sometimes. We're seen as pushovers to assholes like Mendes and De Gea.