In my opinion, we need a holding player to give security for Pogba when he breaks forward and can't get back into position. It seems to me that he cannot work in a two man midfield as he can't seem to recognise when it is appropriate to go forward in a Mourinho team and system. We are generally a possession based team, stemming partly from a two year philosophy of Van Gaal's (which in itself is difficult to progress from), and a pressure to dominate from supporters, media and our modern history of success. For this reason, I think we need a holding midfielder that can control possession, has positional discipline and tactical nous, of which, we have limited options.
Holding midfielder - Carrick / Blind / Herrera / Schweinsteiger
Generally against opponents that we are expected to beat, or indeed any home game, I'd want to see one of the above. I think this much is fairly obvious. I wouldn't be averse to seeing Fosu-Mensah play if we are expected to be under a lot of pressure. He certainly has the physical attributes to provide a decent screen against tougher opposition, but is still lacking the discipline and concentration for a full time role.
The position alongside Pogba, a little further up the pitch, is where our options seem far greater. If we want to truly dominate, a pressing game is key. This is where Schneiderlin is in his element and should be used against a physically strong midfield. If, however, we need more control and creativity, Herrera can play the pressing role almost as well. If we need additional height, both in a defensive or attacking sense, I think Fellaini can be used. He can't press like the other options, but he's an intimidating proposition and I think he could be a real threat given the additional license to attack that a holding midfielder affords. Alternatively, with the extra stamina and explosiveness, I could see Fosu-Mensah performing a similar role. If we are looking likely to easily dominate, the more creative players such as Mata, Mkhitaryan or Rooney can be utilised here, but I would be less inclined to go via that route, unless we are chasing a game.
Central Midfielder - Herrera / Schneiderlin / Fellaini / Mata / Mkhitaryan / Rooney
This is all fine, assuming we play a 4-3-3, a formation that Mourinho is recognised for. However, with the attacking full backs that we possess, along with Mourinho's attacking intent to play a narrow front line, I wouldn't mind a change to 4-1-2-1-2. A diamond midfield, in essence, that also allows us to play our most in form player in his natural position, whilst also taking some of the running from Ibrahimovic. The options that I am mostly interested to see are:
De Gea
Valencia - Smalling - Blind - Shaw
Carrick
Herrera - Pogba
Mkhitaryan - Rashford - Martial
and
De Gea
Valencia - Smalling - Blind - Shaw
Carrick
Herrera - Pogba
Martial*
Rashford - Ibrahimovic
* Or Mata/Rooney/Mkhitaryan
The team needs to be built around a spine of Blind, Herrera, Pogba, Martial and Rashford, going forward. We have enough experience in one or two of Carrick, Rooney, Ibrahimovic and Valencia, as well as maturity in De Gea, Blind, Smalling, Mkhitaryan and Herrera. Currently, our team lacks energy and legs in central areas, dynamism in transition/attack, and pressing in the defensive phase. A spine of Fellaini, Rooney and Ibrahimovic just won't do, and it's preventing Pogba the space that he needs to thrive.