Manchester United: box-to-box midfielder
The biggest problem facing Ole Gunnar Solskjaer is how to play with fluency and purpose when up against a deep-lying defence. United perform relatively well if allowed to sit back and counter-attack via Marcus Rashford and Anthony Martial, but have no idea how to pick a lock.
This is largely because Solskjaer isn't coaching automatisms in training - ways of syncing that become muscle memory - and so they need an individual who will both create chances and, more importantly, sew together the lines of defence and attack. Ander Herrera was an important player when United were flying shortly after Solskjaer arrived. They could do with a more creative version of the Spaniard.
One possible signing is Kai Havertz (priced at 17/2 to join before February 3), but better still would be a hard-working playmaker they could mould into this role - Jack Grealish (7/2) has that potential - or an established Premier League star such as Christian Eriksen (6/1).
Mikel Arteta is doing a superb job so far of getting the team organised and improving individuals with detailed instructions. Their collective compression of space between the lines, achieved via a high press, is simplifying roles and therefore bringing the best out of the likes of Lucas Torreira and Granit Xhaka.
However, playing with such a high line - and continuing to pass out from the back - is proving problematic with centre-backs who lack the pace to cover or the self-belief to continually push up the pitch. What Arsenal need is true leadership in defence; confident ball-playing defenders who will help organise those around them.
This type of player is incredibly hard to come by. Jonathan Tah of Bayer Leverkusen seems a good fit, as does emerging talent Nico Elvedi, who is excelling at Borussia Monchengladbach. Samuel Umtiti (6/1) is probably out of their range.
There are lots of areas of Jose Mourinho's squad that need a major revamp. He is looking for a central midfielder, a centre-back, and a backup striker, but before any of that happens Tottenham ought to replace Serge Aurier at right-back. His numerous errors are a problem, but more importantly Mourinho needs a solid back four and an attacking threat on the overlap for his tactics to take hold.
At their peak Spurs benefited from flying full-backs, and indeed since arriving in north London Mourinho has put Aurier in very advanced positions on the right wing. Unfortunately, Aurier just isn't good enough to provide the penetration, while the Spurs centre-backs are repeatedly caught out by long balls into the channels that catch Aurier too high up the pitch.
Ricardo Pereira is surely the perfect choice. Signing him despite the high transfer fee is an early test of whether Daniel Levy has learnt from his mistakes. The fact Gareth Bale is 2/1 to sign this window suggests the club's priorities lie elsewhere.
Everton: defensive midfielder
For the time being Everton look a little unsure of themselves under Carlo Ancelotti, picking up points but rarely playing with self-assuredness. That is largely because their midfield is brittle without Jean-Philippe Gbamin, the man who was doing an OK job of replacing Idrissa Gueye. Ancelotti's first act in the window should be to find a robust midfielder who can lead from the centre, organising more erratic players like Tom Davies.
He has the bones of a good young side, and if Everton can grab another striker or winger to improve their creative output all that the Toffees will be missing is an assertive midfield presence. Given that Ancelotti is known to take a back seat in terms of coaching, the individual players need to be resilient and intelligent to work out the details for themselves.
Perhaps Nemanja Matic (16/1) could work in the short term. There are reports that Inter Milan's Matias Vecino has also been approached, although he doesn't quite have the right defensive attributes.
Aston Villa: striker
There aren't too many things wrong with the way Villa are set up, and Dean Smith's switch to a more defensively solid 3-5-2 appears to have strengthened their resolve against fellow relegation candidates. For Villa to win four or five of these six-pointers and survive, they just need to find a way to convert the chances created by Jack Grealish. Wesley's injury has put them in a spot of bother.
Douglas Luis and Conor Hourihane have stepped in well for John McGinn while Pepe Reina can help Tyrone Mings organise the defence, plus in a 3-5-2 Villa are less reliant on their wingers running at opposition full-backs (which is just as well, given neither Anwar el Ghazi nor Trezeguet are good enough). Villa simply need a forward who can hold up the ball and score goals.
Christian Benteke (5/6) could be revitalised by a return to Villa Park. He would receive a hero's welcome, potentially inspiring a return to form for a player who is particularly affected by confidence. Other solutions include Michy Batshuayi (5/4) and Glenn Murray.
Eddie Howe has seriously missed David Brooks. Bournemouth are the joint lowest scorers in the division with 20 from 22 matches, partly because Dominic Solanke hasn't worked out but mainly because the manager is wedded to a 4-4-2 formation that relies too heavily on counter-attacks down the wings.
Instead, Bournemouth should try to rediscover their patient possession football, building steadily through a more creative midfielder. This would in turn solidify central midfield, a porous area of the pitch in need of a third body. Without Brooks, Howe's options are limited and Bournemouth's attacking lines have gone stale.
There are some suggestions that creative forward Jarrod Bowen (20/1) is a target, but like so many in-form Championship players reports indicate Bournemouth are not prestigious enough to land his signature.