Let’s see if we can point a few clubs in the right direction. The January transfer window is upon us, which means that at least one club is likely to do something very stupid. Recruitment is hard, and doing it well involves a lot of factors, of which statistical analysis is just one. Nonetheless, what we can do with the numbers is identify teams’ obvious weaknesses in their current squads, and point to the sorts of things they should be looking for in new signings this month. Let’s take a look at five Premier League clubs.
Manchester United: someone not named Paul Pogba who can move the ball forward
For all the noise, Manchester United are a thoroughly ok football team. Defensively, they are sound, putting up numbers all but level with Liverpool in terms of expected goals conceded per game. 
It’s at the other end where things are less interesting, with their 1.26 xG per game just a hair above league average. The problem might be in the construction of the squad. The attack is built around Marcus Rashford, Anthony Martial, Daniel James and frequently Jesse Lingard. All offer speed running in behind, and United can pose great problems to teams on the break, but there is little imagination when the game is played in front of them. The midfield options of Scott McTominay, Fred, Andreas Pereira and Nemanja Matić provide a fair amount of industry but little guile. The only person in the squad who really possesses the creative passing needed to break down teams is Paul Pogba. In his limited minutes this season, Pogba leads United in both deep progressions and open play passes into the box per 90. When he’s on the pitch, he is how Ole Gunnar Solskjær’s team move the ball forward. Even if Pogba was expected to start regularly for United for the next decade, they need more creative passers. As it is, with all sorts of noise about an exit and the possibility that he just won’t play much more football at Old Trafford, they’re desperate. What's less important is who this comes from. United could bring in a classic number ten, or a deeper-lying playmaker, or a wide midfielder who can influence the game. They just need someone, anyone, who can break teams down.
Crystal Palace: someone not named Wilfried Zaha who can move the ball forward
Crystal Palace have much of the same problem at a lower level. It sometimes seems like Roy Hodgson is physically incapable of turning out a side that doesn’t get the basics of defending right, and they’re putting up midtable numbers on that side of the ball. It’s the attack, though, where things look horrible. Palace’s 19 goals scored is the second-fewest in the top flight, and xG does them no favours, suggesting they’re right around where they should be. 
There’s a real case to be made that Jordan Ayew isn’t good enough to be Palace’s first-choice striker. But I’d argue the bigger concern is that Palace don’t have anyone other than Wilfried Zaha to work the ball into dangerous areas. The Ivory Coast international is outdoing even Adama Traore in successful dribbles per 90, while leading Palace by a lot in open play passes into the box. Hodgson has done well teaching this side to keep a compact shape, making sure the spaces between the full-backs and centre-backs and all that good stuff is right, but in possession they have just one idea: give it to Wilf. Zaha might be forgiven for his few goals and assists when he has so much else to do. 
Palace need to find a way to share the ball progression without breaking down Hodgson’s shape. Max Meyer could’ve fit the bill, but has been a big disappointment playing on the left of the midfield. As it is, the last time Palace really had this sort of option was during Ruben Loftus-Cheek’s loan in 2017–18. If someone of roughly his mould could be found, it should help Palace significantly in moving the ball into dangerous areas.
Tottenham Hotspur: a defensive midfielder
Perhaps the most surprising thing in the numbers about José Mourinho’s time at Tottenham Hotspur Stadium so far is that he seems to have built a solid defensive shell. They’ve managed to concede 11 non-penalty goals from 6.98 xG, but other than that, the numbers at that end are a stark improvement compared to the end of Mauricio Pochettino’s reign. 
Mourinho has been able to do this without much of a functional midfield. Tensions between the two aside, Tanguy Ndombele has looked an exciting forward passer when on the pitch, and Mourinho has found roles for such players in the past. Of course, this has typically been alongside a robust holding midfielder, such as Matić partnering Cesc Fàbregas. With the current candidates for the number six role consisting of Harry Winks, who offers calm passing and little presence in front of the back four, and Eric Dier, whose physical limitations seem increasingly insurmountable, Mourinho can’t field Ndombele with proper protection. This leads Spurs to play a lot of pretty dreadful stuff, muddying up the game to keep things ticking along. (I’m sure you’re all shocked that Mourinho would do this.) So bringing in a high-quality holding midfielder would improve the defence and the attack, giving the side a more secure base from which Ndombele and others could really do their thing and dominate football matches.
West Ham: a defensive midfielder
Famous team in London, shiny new stadium, no midfield control. There’s no way around the fact that West Ham are a bad football team. They’re not great in attack and terrible in defence, conceding an alarming 1.66 xG per game. David Moyes has obviously been hired to tighten the Hammers up, and he’ll likely take the same tack as fellow traveller José Mourinho and make them unwatchable in the process. He’d be wise to realize the biggest reason why Manuel Pellegrini failed was the lack of midfield control that enabled him to assert his attacking style on teams. If you want your midfield double pivot to win the ball back, Declan Rice and Mark Noble don’t really do that. When looking at West Ham players’ tackles and interceptions per 90, Rice is a reasonable but not exceptional contributor while Noble falls below more attacking players Pablo Fornals and Felipe Anderson. It’s just not enough. 
Moyes has failed in previous clubs due to an overreliance on experienced British pros. The same mistake must not be made here with Mark Noble; instead, an adequate replacement should be at the top of his shopping list.
Chelsea: don’t do anything stupid
Frank Lampard made a flying start to life back at Stamford Bridge before enduring a difficult winter. The numbers show Chelsea to be a really good side, third-best in xG difference per game, yet they've suffered a fairly brutal number of goals from the shots they’ve conceded. 
Some of this can be blamed on Kepa Arrizabalaga and his long-term below average shot-stopping numbers, but the model estimates he has only conceded 2.26 goals more than expected this season. The rest of his underperformance can be blamed on other factors. Predicting future xG under- and over-performance is always a crapshoot, but the most likely scenario is that it gets at least a bit better. Chelsea are good and should trust in themselves. Which is why it makes it all the stranger that the rumours are of them going big this month. Resigning Nathan Aké would be a reasonable move, with centre-back options often looking thin given Antonio Rüdiger’s frequent injury problems. Emerson Palmieri and Marcos Alonso both look prone to errors at times, so a long-term solution at left-back is entirely justifiable. But making further radical changes to the attack is not. Talk of Zaha and Moussa Dembélé abounds, with both seeming like outright downgrades on what Lampard already while requiring serious cash. Jadon Sancho is certainly a big talent, but the cost of extracting him from Dortmund is gut-clenching when the club already have good young talents in the wide positions in Christian Pulisic and Callum Hudson-Odoi. Chelsea have really promising talents that have shined through the transfer ban. Don’t mess it all up just because you can.