Premier League 2018-19: 3 reasons why Manchester United are likely to finish outside the top 4

Manchester United have had a tumultuous season. They had a rocky start under the management of Jose Mourinho, and Mourinho was eventually sacked and replaced by caretaker manager Ole Gunnar Solskjaer.

The team's performances experienced an incredible improvement from there and United were playing smooth, attacking football. Their unexpected comeback against PSG in the Champions League prompted the club to appoint Solskjaer as the permanent manager.

However, ever since Solskjaer's new contract has been signed, United's performances have dropped dramatically. There a few reasons that have contributed to their failure to perform on the Premier League stage, and that could cost them a spot in Europe's top-flight competition.

Here's a look at three of those reasons:

3. Sub-par squad quality and depth, primarily in defense

Quite simply, Manchester United have a sub-par squad. Their defense is in shambles.

Phil Jones and Chris Smalling would be unlikely to start in any other top 6 Premier League team. Ashley Young is a major liability and gives the ball away, on average, over 15 times a game.

Victor Lindelof is the only saving grace for the defense, but he cannot shoulder all the responsibility by himself. He needs a strong centre-back partner and United will be looking for one (Kalidou Koulibaly and Toby Alderweireld are rumored to be at the top of the list) when the summer transfer window rolls around.

Eric Bailly has the potential to be United's other centre-back to partner Lindelof, but is too rash and inconsistent to be so right now.

Additionally, the front line does not have enough support, as seen when Anthony Martial and Jesse Lingard were injured. Romelu Lukaku can come off the bench, but that forces Solskjaer to shunt Marcus Rashford off to the right wing, where he is far less effective.

Solskjaer will definitely be looking to add strong players to the bench in the summer. He will also want to sort out his midfield and judge whether the currently ineffective Fred and Andreas Pereira should be sold.

2. Underperforming attack

Manchester United v Chelsea FC - Premier League

United's defense leaves much to be desired, with a significant lack of quality to protect keeper David De Gea. As the defense cannot be relied upon, the attack must perform well to outscore the opponents on the other side of the field.

Most clubs would love to have even one of United's attacking players. United boast of Marcus Rashford, Anthony Martial, Paul Pogba and the much-maligned but quite talented Romelu Lukaku. However, in recent games, especially after the announcement of Solskjaer as permanent manager, the attack has underperformed.

With the defense leaking goals at one end and the attack severely misfiring at the other, United have lost numerous points. There is also a lack of firepower on the bench. Additionally, the midfield lacks offensive quality.

Ander Herrera and Nemanja Matic are more defensive and Pogba is arguably the only midfield player who can break defensive lines with precise passing. Solskjaer will want to add another player or two that can connect the midfield base with the attack and feed balls to the front three.

1. Mental weakness

Manchester United v Manchester City - Premier League

The Manchester United squad has been accused of being weak mentally. There is seemingly a lack of desire to win, as evidenced from the fact that several United players were jogging half-heartedly on the pitch during the 4-0 drubbing at the hands of Everton.

When United were playing beautiful, incisive football, the players were happy and effective. However, when faced with tougher challenges, the red half of Manchester has been unable to buckle down and grind out results, even if they are not playing at their best.

Additionally, Alexis Sanchez's incredibly high wages have caused other members of the team to rethink their own options and wages. David de Gea reportedly wants to be paid on par with Sanchez. The club is unwilling to do so and, as a result, De Gea may seek a move away from United in the summer.

Manchester United are a huge club with an amazing history. They do, however, have a lot of issues they need to fix before they can challenge for the title and Champions League again.

Some will be solved easily, such as the buying of a world-class centre-back. Some challenges, such as Solskjaer instilling a winning mentality and stronger backbone, will be more difficult.

Manchester United will likely be a force to reckon with next season, but this year, the club will remain out of the top four and will play in the Europa League next year.