Erik ten Hag led the Red Devils to their worst finish in Premier League history in the 2023/24 campaign.
Despite being given a one-year contract extension in July, the Manchester United hierarchy opted to sack the Dutchman and they've moved quickly with the appointment of 39-year-old manager Ruben Amorim, formerly of Sporting CP.
We take a look at the impact this appointment may have on the existing United squad.
Position: Central defender
Since making the move to England, the Argentine international has struggled to make a name for himself the way he would have liked.
Under Ten Hag, Martinez primarily played on the left of a two-man centre back partnership. However, the arrival of Amorim may see his role change.
In his time at Sporting Lisbon, the Portuguese manager has opted to set up with three central defenders. Martinez would likely play on the left of a back three.
In this role, he will be able to demonstrate his on-the-ball ability, as he will be better positioned to play more direct passes into the centre forward, whether it be Rasmus Hojlund or Joshua Zirkzee.
The former Ajax defender often gets criticised for his impulsive style of play. Amorim's system will likely help cover Martinez's weaknesses, receiving greater protection from the central and right-sided centre backs, as opposed to having cover by just one defender in Ten Hag's system.
Position: Defensive midfielder
The appointment of Amorim will see him reunite with Uruguayan midfielder Manuel Ugarte. Under Amorim, Ugarte earned himself a move to PSG, where he struggled to hit the ground running, playing just 25 times for the French club.
Ugarte's defensive positioning and ability to do the simple things efficiently will be crucial in Amorim's start to life at Old Trafford. Not only will it provide greater protection to the back three, but it will also free up a more advanced role for his predicted midfield partner, Kobbie Mainoo.
If Amorim can get the 20-time Premier League winners playing the way he wants, expect Ugarte to be a significant contributing factor, thanks to the quality he will provide both on and off the ball.
Position: Defensive midfielder
With United depleted in the midfield area, Casemiro may be forced into action at the start of Amorim's reign. However, don't expect him to be a permanent starter in the team.
The way that Amorim sets up relies on his central midfielders to cover a large amount of ground, due to the gaps that are created through the setup.
While this may benefit the likes of Ugarte, Bruno Fernandes and Mason Mount, Casemiro's performances in recent years suggest he might not have the required energy and legs to work in this system, especially in open games against better opposition.
Position: Centre forward
The Dutch number 11 has already been handed a tough start to life at the Red Devils, unable to find form in front of goal.
Things might be about to get even harder for Zirkzee. Now, there is no denying that Zirkzee is a technical centre forward who thrives best with his back to goal when he is linking up play. However, knowing the way Amorim sets up, it is hard to see how the former Bayern Munich prospect will break into the starting XI.
Zirkzee faces competition in the form of Rasmus Hojlund, a fearless striker who likes to break in behind the opposition's defensive line, whilst also possessing the physical attributes to hold off imposing central defenders.
Amorim's preferred centre forward at Sporting Lisbon, Viktor Gyokeres, shares many similarities with Hojlund, suggesting Hojlund will be nailed on to start under the Portuguese manager. This begs the question as to where Zirkzee will fit in.