At the very least, considering his age, experience, the fact he's an Italian international and his passing abilities. We should get 10M minimum for him.
We know his flaws better than most transfer directors do. If somebody like Monaco were to buy him, they would not see his idiotic bursts unless they followed him closely for a long time
Oh, and our goals against record has been one of the finest in Europe for 2.5 seasons now. So, there's that too.