Without selling anyone I suspect we will only get a central mid.
Looking at the squad depth United have had the last 7/8 years there seems to be a very clear squad format they try to utilize. We are in most areas very close to the "mould" they try to fit the squad into.
At CB, if we count Tuanzebe as an option, we are 1 player over what we have had for most years. Most years we have had 5 options (Vidic,Jones,Smalling,Evans,Rio or now Rojo,Jones,Smalling,Bailly,Lindeløf+Tuanzebe).
Considering the wages most of our "squad" players are on, I wouldn't be surprised if we go into next season with the centrebacks we have now unless we sell someone.
Backs, 4 options (2 each side). Some years we have had a 3rd option on each side, like Buttner or Fabio.
At CM, we've had 7 or 8. Currently we are at 6 (Pereira,Pogba,Mata,Matic,McT,Fred), so this is where it looks most likely with a new signing.
Out wide, we've had 4 most years. With James in, were at 4 again (Lingard,Martial,Alexis,James)
At ST, we've usually had between 4-6 players. Going from 4 to 2 makes sense, since we are now only using 1 striker formations. But this should be notable in terms of more players in other positions, especially centrally, but it isn't. We've cut away a Berbatov, Rooney and Chicharito but never bought another player in another position to compensate.
Of course I hope we sign a CB, two CMs and another attacker. But looking at the squad depth, and the rumours of Ole wanting to give youth gametime, the rumours of United having to sell before buying seem very logical.