Can't pay the kind of money he'd cost for a player who's injured 1-2 months every season. It's just not an option.
Beyond the money itself, he'd be coming here expecting to be a starter whenever he's fit. That's all well and good when he is fit, but if you build your team around a player who's routinely injured, it simply costs points every season because of the unrest it creates. It means you have to adjust your system too often, and that's not a stable situation. You do not build a team around injury-prone players, end of story.
There's a reason he's not a core player at Real Madrid and didn't start the CL final even though he was fit. We can't do what Real Madrid won't do if we want to get back to that level.
Besides, injury-prone players don't tend to age well and he's 29 next month. We can't keep signing big names who are nearing the ends of their careers. It's short-sighted.