We need an intelligent central midfielder. Much more than anything else.
The basis of the dominating Juve was the midfield - Pirlo, Vidal and Marchisio. Once we added Pogba and Tevez, the team became a European force. The defense was good and it's still the good old, but the midfield was the most important part. Once we lost Pirlo and Vidal, problem's were expected. But with Marchisio gone injured and the only new quality arrival in midfield being injured too (Khedira), we couldn't expect a better start to the season, even if we had superior attackers and defenders to those we have.
Stats in serie A expectedlly support this, because we have 9-2-0 record when at least one of Khedira and Marchisio plays, and it's a 1-1-4 record when both were gone (a win against a 10 men Genoa and a draw at home with Frosinone).
Basically, we're walking on thin ice with the midfield. With Khedira's injury record, we're a Marchisio injury away from the nightmare in August and September. It won't matter how good Dybala and Mandzukic play if we play Padoin, Hernanes, Sturaro and Lemina in midfield. With Pogba playing in a more advanced position and Dybala doing really well in that AM role, I wouldn't go with an AM, I'd do my best to secure a top quality CM. Moutinho and Gundogan look really attractive right now for this team. In Marotta's place I'd make it my top job to secure one of them this winter.