He never once used that lineup last season, players or formation. He doesn't really like 3 at the back. Even when Juve fans were calling for it in some moments he stuck with 4 at the back.
With current team, no signings, my guess is he would play either 4-3-3 or 4-3-1-2:
DDG
AWB-Lindelof-Maguire-Shaw
McTominay-Matić-Pogba
James-Martial-Rashford
or Mata behind Martial and Rashford.
If you want to read more about Allegri, there was an excellent interview yesterday at a conference in Poland with him. It's in Polish, but very easy to understand through Google Translate.
I posted it in another thread yesterday but it got lost 2-3 pages back while waiting for mod approval.
Here it is:
Thanks. However I've been following Allegri since his time at Milan. What irks people is specifically why big clubs love him. Allegri is a scavenger who adapts tactics to the players he's got, whose not afraid to change system and play players out of position when its suits him and who don't give a feck about what fans say and instead focus on the results. That pisses of the fans who wants a well defined way of playing football that they can relate to, who sees his versatility as indecision and who want to see their team hammering opposition even if that translates in less points
If you ask me Allegri will use plenty of formations while with us from this formation
-----------------------DDG-----------------------
AWB-----------Lindelof-----Maguire--------Shaw
----------------------Mctominay----------------------
------------------Fred----------Pogba-----------------
Jesse/James-------------------------------------------Rashford/Martial
-------------------------Martial/Martial----------------------------
Allegri loves movement and workrate in CM. He also love a hardworking inside forward (Mandzukic/Teves) alongside a more creative winger (Costa for example)
However he could easily go to this formation
-------------------------DDG------------------------
-------------AWB--------Lindelof--------Maguire------------
Dalot------Mctominay-----Fred------Pogba--------James
---------------Martial--------Rashford
or even a narrow 4-4-2
-----------------DDG--------------
AWB-----Lindelof-------Maguire---------Shaw
-------------------Periera----------------
------------Fred-------------Pogba--------------
-------------------Jesse/James-----------------------
--------------Martial--------Rashford------------
or a narrow 4-2-3-1
-------------DDG-------------------------
AWB-----Lindelof-----Maguire--------Shaw
----------Fred-------McT---------------------------
----Jesse---------------------James/Martial----
---------------Pogba------------------------
--------------Martial/Rashford-----------------------------
His first transfer will probably be a powerful striker upfront. He always had those whether its Ibra, Higuian, Mandzukic, Ronaldo etc. Its important to have a forward whose able to attract attention so he can create space for the inside forwards (one is usually a converted striker whether its Tevez, Dybala or Mandzukic) to go in the box and score goals.