I gotta agree with rakib here, we shouldn't add another midfielder to our team, and if we do it should be an AM. We have so many options that it just doesn't makes any sense even if Pirlo leaves. I'm not one of those who keep undervaluing depth or keep trying to say how awesome Asamoah would be as a CM. But really we don't need anyone else in this area, we have Marchisio, Pogba, Vidal, Pirlo?, Khedira, Sturaro, Pereyra and even Padoin, and yes, Asamoah can also play there. That's 9 possible midfielders, and yes we do use a formation were we use 4 of them at the time, but it's not black or white, it's not a 100% change every time we rotate the team, some wilm play twice in a row, some will not, it doesn't has to be team A or team B but more like a mixture of both as we've seen this entire year. Injuries can also play a big part but I'm sure that we have enough quality to keep moving forward, as we did this year when Vidal wasn't sharp, or when Pogba was out.
And even if we're short on midfielders, there are other formations which we also use which don't need 4 midfielders, we've the fan favorite 352, we have 4321 with Dybala and Tevez or what about a 433 with Berardi, Coman or even Dybala on the wings. Sounds good? Nice.
If Pirlo leaves then we might probably need another CM. Or if Tevez leaves then we definitely need an AM. But as of now, if we gotta add something to the midfield then lets bring in an AM, Oscar/Firmino/Eriksen/Özil/Isco whatever, let's bring some magic and let's make Allegri's wish comes true.