I don't know why people are calling Verratti a defensive liability, he's not a traditional regista a la Pirlo, he some parts of the game is infront at the defense, but he normally occupies a position akin to Xavi's role, and this season he has been maybe the best performer in league and in europe alongside Zlatan. He is the key to their possesion-based style, and also playing alongside two defensive-minded midfielders help him a lot (Motta and Matuidi).
He would have those type of players if he came here (Vidal, the best in the world in this type, Asamoah and even Marchisio) so he would 't suffee a lot defensively, especially because of the improvement he had this season.