#2 Man-marking and positioning
This has been a huge problem for the Red Devils. Solskjaer has introduced a system of playing out from the back like what Manchester City, Barcelona and Chelsea under Maurizio Sarri did last season. It is clear that United players are not comfortable under the ball but are yet to be caught out. When the nature of opposition improve then they may be pushed back into their own territory which creates room for mistakes to happen.
To counter this, better man-marking and positioning is imperative, Consider the Crystal Palace game, for example. Maguire should have been better positioned the first goal as the last man to cover any loose balls that evaded Victor Lindelof.
This also applies to the second goal that they conceded. Positioning and man marking helps to anticipate the danger and gives players a better chance to deal with those situations. With these adjustments, United should display a better brand of football than what we have been accustomed to in the post Sir Alex Ferguson era.
#1 Formation
It is no secret that Ole Gunnar Solskjaer has set his team under variations of a 4-3-3 formation since the start of the season. He banks on the pace and youth of the front three to look for goals. When this fails, then the team is in trouble in terms of being vulnerable defensively. So much speed and energy is spent on the counter that the team is exposed when they lose the ball. Full back Aaron Wan-Bissaka pushes forward a lot and so does Luke Shaw.
In a 4-3-3 formation, with Pogba and Scott McTominay as central midfielders, United are vulnerable defensively because they do not have a midfield protector. The one player who could have done the dirty work, Ander Herrera, was shipped to France after contract negotiations broke down. Matic, the other viable option in midfield, is past his peak.
Solskjaer needs to fix this by switching to a 4-4-2 when defending and 4-3-3 on the attacking. How this can be achieved is by having a dynamic midfielder like Fred come in to support Pogba and McTominay. By doing so, he will free Pogba to do more Pogba-like things such as joining in the attack, assisting and scoring.