Fucking ridiculous, man.
I'm realistic. I'd like to say "offer us £25m+ and we might accept", make them pay over the odds and so on, but left backs don't tend to go for that much, even though in my biased opinion, he's worth more than that and is easily one of the best left backs in the world. He'll go for about £19m I reckon.
If this all sounds like it's an inevitability, that's because it is. We've all seen this story before and we all know how it ends, and it doesn't matter how 'level-headed' and 'professional' the player is. They offer a vaguely decent amount, he'll go. The best clubs just hoover up the talent from other clubs. It's sickening but it's true and will continue to be the case.