If I said Higuain was impossible at the start of the mercato then Nainggolan for next summer needs another word inventing for it. But he's exactly the sort of player who would add something to us. Those are few and far between in Serie A. If we are looking at potential starter/rotational players from Serie A then the list is pretty short:
Goalkeepers - Handanovic
Defenders - Manolas, Koulibaly, Bruno Peres
Midfielders - Nainggolan, Hamsik, Allan
Forwards - Icardi, Insigne
Add in a bunch of younger players such as Perin, Donnarumma, Romagnoli, Hysaj, Diawara, Zielinski, Bernardeschi, Berardi etc, who in the future may have starter potential.