#1 Competition
The battle for the Premier League top places is on fire. Other big clubs in the league either did some investment in the squad or have found their rhythm. With the current United squad, it will be very difficult to crack the top four positions. Their competitors have depth and quality players in various positions.
On paper, Manchester City, Liverpool and Chelsea already have vastly superior squads. This has reflected on their style of play and their league position. They all look like serious title contenders. There is Spurs and Arsenal who also have strong sides. United have struggled to win against smaller sides and there is no foreseeable way out of this jigsaw puzzle if things remain the same.
There is quite simply a lot of competition from big and smaller clubs. United seem to have a real test on their hands. Truth be told, things do not look pretty at all for the United and only a Zidane-like shot in the arm (as he did in Real Madrid) can dig them out of this hole.