He's joining a Premier League team on a hefty wage, be it this window, the next, or next summer. A contract will only increase his value, which may price teams out and stop him getting his Premier League move (and FAR more money). We are selling now for £25m, which is close to being hit, why enforce himself a £30m?
The odds of him sustaining a career ending injury is incredibly low. I would have thought that's obvious.