This is the time for Ruben Amorim to change to another formation, if he does not want to say goodbye right after the match with Chelsea if he loses weakly. With the current players, his Man United can play 4-2-3-1.
Goalkeeper: Senne Lammens
Man United's transfer department once missed the opportunity to sign a goalkeeper who won both EURO and the Champions League, Gianluigi Donnarumma, to replace him with Senne Lammens.
Having to sit on the bench will not help Senne Lammens mature, especially when he only sat and watched Altay Bayindir play soullessly and ineffectively every week.

Right-back: Noussair Mazraoui
Mazraoui is a modern defender, solid in the competition, strong in the air and plays a full role as a full-back. He was much more effective when deployed as a right-back instead of a wing-back.
Central defenders: Matthijs de Ligt and Leny Yoro
De Ligt is one of the few successful signings under Erik ten Hag. The Dutch midfielder is a sturdy shield, full of strength and fitness. Like many other centre-backs, he felt comfortable standing in a four-man defence.
Besides De Ligt, Leny Yoro is a rare spark of hope in the gloomy sky of Old Trafford. The French star is agile, intelligent and has excellent coverage, bringing a rare peace of mind to the defense this season.

left-back: Patrick Dorgu
The recent Manchester Derby clearly showed Dorgu's limitations when asked to attack. In contrast, speed makes Dorgu a reliable shield on the left flank. Meanwhile, Luke Shaw will find it difficult to return to his peak after injuries.
Defensive midfielder: Casemiro
Casemiro is no longer as satisfied as before, his speed and fitness have declined. However, in the context of Man United not having any better defensive midfielder, he is still a mandatory choice. Not only does he pass the ball, the Brazilian star also knows how to compete in the air and occasionally scores from set pieces.
Central midfielder: Kobbie Mainoo
In a short but very positive performance against Man City, Mainoo brought calmness and a desire to express himself. Amorim has criticised Mainoo for his lack of pace, but Paul Scholes has also been labeled slow before. The problem in the Man United midfield is the quality of play, not the players running fast or slow.

Right striker: Bryan Mbeumo
Mbeumo's volley against Man City showed the Cameroonian striker's worth. If the one standing in goal had not been Donnarumma, the ball would have been in the net.
However, a big problem is that Mbeumo does not get the ball regularly. Man United's ability to rotate and progress the ball is really having problems.
Middle blocker: Bruno Fernandes
Bruno Fernandes is not the type of midfielder who specializes in disputes or pursuits. He was forced into inappropriate roles, leading to situations where he neglected his opponents, such as situations where Phil Foden comfortably scored.
Forcing his best player to play in the wrong position is perhaps the clearest self-dismantling in Ruben Amorim's entire philosophy.

left striker: Matheus Cunha
The Brazilian star can drop deep to support the midfield when needed, and is also a sharp attacker in the penalty area. Using Cunha as a left striker will help the "Red Devils" have more breakthrough solutions and score goals, instead of forcing him to carry too many unprofessional tasks.
Center forward: Benjamin Sesko
Sesko is 1m95 tall and has an ideal physique for the center forward position. However, the match against Man City showed hopelessness as the ball almost never reached the position he was waiting for.
How can a striker prove his ability if he does not have the ball to finish? Sesko is being turned into a version 2 ofojlund, as efforts become ineffective in a deadlocked system.

A solid back four, a creative central midfielder with Mainoo and Bruno, and a dynamic attack with Mbeumo Cunha Sesko can help Man United regain balance.
This is not necessarily a comprehensive solution, but it is certainly better than continuing to slide in conservatism with a 3-4-3 formation. Amorim needs to act if he is to save himself and the hot seat at Old Trafford.