None of them will 'improve their form' until the team starts functioning as a unit.
We're all human so we want to believe there is a simple solution - hence why you'll see posters pile in on certain players or the manager. They subconsciously want to believe there is a quick-fix...we all do it.
The fact is, many of our players have proven they can perform to at least a 'good' level for other teams or in their national sides. I would say we have very few regular starters who are just outright 'poor' - with the exception of DDG and Dalot, in my opinion.
The rest, we might 'like' or 'dislike'...but at some stage they have all done enough to suggest they can function in a top-half team...even players I don't rate personally like Rashford of Fred.
The major problem(s) we have are as follows....
1) The GK is a throwback who won't leave his goal-line. This puts immense pressure on the defenders because they are asked to play a high-line whilst knowing their GK isn't going to sweep behind them.
2) In addition, our press is ineffective. Contrary to popular belief, you don't need to be quick to play a high-line. You need to be an aggressive, front-front defender who can play up against the CF, win long-balls, intercept passes into their feet and generally push them backwards into their own half. If you're having to turn to chase players back towards your own goal, 99% of the time that's a failing of the system. Unfortunately, our defenders have to turn and chase towards their own goal several times per game because the press is ineffective/chaotic/lacks energy and the GK won't sweep. This is why several international defenders have been tried and yet we continue to ship goals at a ridiculous rate to poor sides.
So....back to my point....posters will talk about Maguire, Varane, Lindelof, Bailly, Martinez etc...being 'poor' or out of form....I tend to disagree, it's just an impossible job right now and they won't 'improve their form' until we solve the problems we have as a unit.
3) The third problem we have is our inability to progress the ball through the midfield. McTominay was always an AM/CF in the Academy and you can see this as he plays in straight lines. He really struggles to play 'on the half-turn' and therefore is highly unsuited to playing a deeper midfield role were he will be expected to receive the ball under pressure. Likewise, Fred is not 'press-resistant' as he also struggles to play on the half-turn. Also, unlike McTominay, Fred is too weak to use pure strength to shield the ball and is easily brushed aside by opponents in midfield duels. Fred also gets himself into a really poor shape to receive the ball...go back to the mistake he made in the Brighton game were he gives it away from a GK and we nearly concede a goal. He is far to 'square'...this is a 'pressers' dream because the player receiving the ball has no idea what's behind him...and even if he does, the only pass he can make is backwards. Until we sign not one, not two but maybe three midfield players who are comfortable on the ball, we're destined to keep passing the ball sideways and backwards and being a wet dream for every team with any kind of loosely co-ordinated press (another reason we keep being tanked by poor sides).
4) The fourth problem stems from the third problem...hence my point about all this being linked to failings of the unit more so than any one or two individuals. The midfield two struggle to progress the ball through a press and end-up going backwards and/or losing the ball far too often. This means our attackers are starved of service, and if they do receive the ball, it's generally from a longer pass and they're disconnected from their teammates. Now, the attackers could certainly help themselves by running and pressing harder and that's something they will have to learn, but it's no wonder they're struggling collectively because we don't find them in good positions and when we do, they've no supporting runs (underlaps/overlaps) from their teammates and the two CMs are probably hiding from the ball, as is their way.
5) Ronaldo and Sancho are slow (relatively speaking) and this means defenders can squeeze our attackers which means the opposition midfield can press higher in-turn. See how one problem leads to another? Our CF is slow, so we get squeezed because teams don't fear his pace. This puts more pressure on our midfield to receive the ball in tighter areas...which we have said above they're not good at. It's like an accordion, you push at one end and the whole thing is squeezed and compressed.
Of course, we have other issues but I believe these are the major problems we face. Yes I have talked about some individuals, but aside from DDG and possibly, possibly Ronaldo, I don't think replacing any one individual would have a huge impact. This is why I am so surprised and disappointed with our transfer business so far. We needed a fast, aggressive CF, two ball-playing, press-resistant CMs and a GK. We got a tiny CB, a talented but not physically imposing AM and a backup LB. None of which address any of the core issues in our team. They could have been the greatest three players in the World but they don't solve any of the fundamental structural issues we have.
What concerns me is this is basic stuff. I like to think I know a bit about the game having watched and played relentlessly my entire life but I'm not someone who sits freeze-framing games or watching tactical breakdowns on YouTube...this is just basic 101 stuff. It concerns me that ETH knew he was taking the job from about March/April yet doesn't appear to have watched any of our games and identified any of these issues. If he did and he still persisted with this team and set-up then I question his sanity.
We would have been far better bringing in six players for £30/40m each that actually address some of these challenges than spending £60m on a CB and trying to spend another £70m on De Jong. FDJ would undoubtedly have been one of the press-resistant midfielders we needed but it's too much budget spent on one area. Sometimes we might have to sign players who are 'stepping stones' to improve the squad incrementally. We have seen the 'big hitters' that come in flop because they are playing in a flawed team.
Summary - we have tactical/structural issues....if one or two players are out of form, that's on them....if an entire team of internationals look like pub players every week, getting hammered by Brentford, Brighton and Watford....that's structural/tactical