As the January transfer window draws to a close, we take a look at the worst-case scenario for each and every top club in Europe.
Which clubs can't go without reinforcements, who would be loathe to lose one of their current crop and who appears royally done for on paper?
We've stuck to Opta's top-five leagues as a guide, so please don't take our loose definition of "top" as gospel. There are a few bonus balls added in at the start for good measure!
An injury to Artiz Aduriz could stunt the team offensively. Kike Sola has been extremely underwhelming.
How will the club fare without Nemanja Matic? An Enzo Perez injury could really shake things up.
The home form cannot afford to nose-dive, as their away form hasn't been strong. Near-perfection is required to land in second.
Anything that rocks the ship is bad news for Roberto Martinez. Everything is going so well.
Giuseppe Rossi has already gone down, and Vincenzo Montella's side has recovered. Could they do without Borja Valero, though?
If nothing changes (from a managerial standpoint), Jackson Martinez will not be able to keep them afloat in the title-race single-handedly.
For Real Sociedad, see Everton: everything is going swimmingly at the moment, so they'll be hoping for a strong run-in.
Their academy-bred Portuguese midfield trio getting torn apart by suitors would give socios nightmares.
The Tim Sherwood express runs out of steam, Emmanuel Adebayor loses interest and Erik Lamela never, ever comes good.
Mateo Musacchio decides to move one window too early.
Arsenal need to pick up at least one body this winter, or when the UEFA Champions League returns, they'll be vulnerable amid a chaotic schedule.
Olivier Giroud and Lukas Podolski can rotate in the striker's role, but if one gets injured, is Nicklas Bendtner trustworthy? Julian Draxler isn't required, but a player of some sort is.
Bacary Sagna, given his form this season and his leadership skills, is a priority for Arsene Wenger to sort out. For the Frenchman to sign his future away on a pre-contract to someone else would be a crushing blow.
Atletico Madrid have an astonishing array of talent, and it's widely acknowledged that some of it will move on during the 2014 summer window.
Koke has had his contract (and release clause) upped twice in the last eight months, Diego Costa looks a goner in 2014 and Arda Turan—among others—will attract interest.
But those are worries for the 2014-15 season, right? Perhaps. Diego Simeone's worst nightmare would be to lose one of his key cogs this month just as his team are mounting a challenge on three fronts.
Aside from the obvious injury concerns surrounding Lionel Messi while Neymar is sidelined, there are some fears residing over the fact that the Argentine is dropping deeper and deeper with every passing week.
If he wants to convert to a No. 10 that's fine, but the problem is that Barcelona will have to adapt to this change by signing a true No. 9 to play ahead of him—or move Neymar/Alexis Sanchez.
It's unclear whether or not Messi's deep role is a product of injury as yet, and only time can tell, but if he converts too soon, it could make for some uncomfortable growing pains at a critical point in the season.
Bayer Leverkusen's worst-case scenario was realised extremely early in the transfer window.
Sidney Sam, a key cog in Sami Hyypia's attacking lineup and consistent producer this season, has signed a pre-contract with Schalke that will see him depart for the Veltins Arena in the summer.
It happens in football, sure, but his buyout was an absurdly low €2.5 million—a product of his injury-prone past—and the Werkself stand no hope of replacing his menace for a similar fee.
Bayern Munich are furiously attempting to extend the contract of Toni Kroos, but no progress is apparent, as per Goal.com.
The world-class midfielder has only 18 months left on his current deal and is yet to commit his future, despite being reared by die Bayern into the wizard he is today.
Losing Kroos would be one hell of a blow, and if he enters the summer with just a year left on his deal, interest from the likes of Manchester United, purported by The Telegraph, becomes a lot more credible.
Borussia Dortmund's season is a write-off due to the inconceivable amount of injuries they've sustained.
It's a real shame, given that this was to be the season BVB hoped they could build on last year's heroics and challenge Pep Guardiola during his first campaign in charge of Bayern Munich.
But forget the title: For Juergen Klopp and his men, it's now about securing UEFA Champions League football for next year amid the tough challenges of Borussia Moenchengladbach and Bayer Leverkusen.
Another long-term injury would likely just make fans of club let out a wry laugh and smile. Disbelief.
Over the first five months of Jose Mourinho's return to Stamford Bridge, he's set about transforming Eden Hazard into the elite match-winner he was always destined to become.
He is now their key attacking cog, best overall player and primary creative outlet, meaning an injury to him would shed focus back onto the under-performing strikers.
Juan Mata didn't fit Chelsea's system, Willian is perfect but he's no Hazard and Mohamed Salah is a project. The Belgian is Jose's new Cristiano Ronaldo.
Internazionale started the season very brightly under Walter Mazzarri, but things are looking a little bleak now.
The Nerazzurri are 11 points off the Champions League pace, can't seem to score any goals and are continually held against lesser sides. They're trying to shift Andrea Ranocchia and Fredy Guarin, but no one wants to buy them, and they've failed to acquire the targets they want in the process.
Something has to give.
There are very few things likely to disrupt Juventus' impressive canter toward a third consecutive Scudetto and potentially historic Serie A season, but losing a midfield jewel is one.
Interest in Arturo Vidal and Paul Pogba is high, with The Guardian suggesting Manchester United favour the Chilean—who wouldn't?—and La Gazzetta dello Sport reporting a €70 million bid for the Frenchman from Paris Saint-Germain has been turned down.
Midfield depth is the one area of suspicion ahead of a tough Europa League schedule in the second half of the season, and losing one of your best players would not be a good start to 2014.
LOSC are going through their own worst nightmare right now, as Simon Kjaer has been a monumental loss for the defence.
The club rely on their sturdy defence, as they are unable to score goals, and if Marko Basa were to go down too, this side could plummet.
On the plus side, Lille are expected to sign Sebastien Corchia from Sochaux—an excellent move for a bargain €3 million fee, as per L'Equipe.
Liverpool haven't given any indication that they're likely to spend this month, but if a top-four chase is truly on the cards, they simply must.
Glen Johnson's form has nose-dived, Aly Cissokho looks...unimpressive, and Jose Enrique gives the ball away far too often in the final third. It's odd to think Jon Flanagan—nicknamed "Flani Alves" by the fans—is the safest option at full-back right now.
Does a Martin Kelly-Flanagan full-back pairing win you fourth? probably not. A physical defensive midfielder, to beef up the central zones and help Steven Gerrard, is a must too.
Manchester City are the current favourites to lift the Premier League trophy at the end of the season, but they are just one or two injuries away from seeing those dreams crippled.
The depth at full-back, advanced midfield and striker is astonishing, but the lack of cover for Fernandinho and Yaya Toure is equally so.
Javi Garcia is not a capable replacement, and Jack Rodwell's fitness cannot be trusted. What will Manuel Pellegrini do if his trusted duo encounter problems?
Juan Mata is a phenomenal signing for Manchester United; fan reaction from the selling club is often a superb barometer, and there doesn't seem to be a single Chelsea fan happy to see the Spaniard go.
He's a world-class player, so that's understandable, but David Moyes has a tough assignment in finding a top-four finish, and Mata should just be the start.
Central defence, right-back, left-back, defensive midfield—take your pick, Moyes, and improve one or two more areas lacking sufficient quality.
Marseille are looking a little flimsy right now, and if one of their key attacking outlets left the club this winter, they'd be in serious trouble for the rest of the season.
Andre Pierre Gignac and Florian Thauvin would be monumental losses, but Mathieu Valbuena—despite looking a little iffy at times—is irreplaceable.
Without a full-time coach and firmly under a sell-to-buy policy, there's no way L'OM could replace like for like when it comes to their star forwards. They'd slip even farther down the Ligue 1 table.
The Milan squad have endured a horrid season, but since Clarence Seedorf was appointed manager in place of Massimiliano Allegri, they've won two on the bounce.
A magic touch? Not quite: the Rossoneri have been a little lucky to accrue six points from those two fixtures, with the Cagliari game in particular seeing two extremely late goals steal a victory.
There won't be any major business done in the final week—the club did their shopping early in the form of Adil Rami and Keisuke Honda—and Milan will just have to hope the "Seedorf effect" reigns supreme for weeks to come.
Radamel Falcao going down with a long-term injury is the nightmare scenario. In this instance, they're similar to domestic rivals Lille.
With or without the Colombian, Claudio Ranieri's troops have been struggling to convince many regular Ligue 1 watchers that they have what it takes to haul in Paris Saint-Germain.
They need to find another striker to shoulder the load in his absence. He needs to be an EU citizen (unless they want to move on a non-EU player for the quota), and it brings the Lacina Traore loan into serious question—no matter how raw he is. Could someone like Fabinho have been moved on for him?
Napoli have a ferocious attack, with the three-headed monster of Jose Callejon, Dries Mertens and Gonzalo Higuain ripping teams to shreds on a weekly basis.
They've even got Lorenzo Insigne to call on, and midfield looks well stocked now that Rafa Benitez has added Jorginho to his collection.
That leaves the defence, which remains as suspect as ever. They're so desperate for a left-back they went in for Kevin Constant, as per Football Italia, and none of the current options partnering Federico Fernandez seem up to scratch.
Yohan Cabaye: Wanted by Laurent Blanc.
Paris Saint-Germain appear to be well aware of their potential problems, with Laurent Blanc moving for Yohan Cabaye this weekend and bidding £14 million for his services, as per the BBC.
It highlights the lack of depth the capital club have in central midfield, and with the 4-3-3 remaining the manager's favoured formation, reinforcements are direly needed.
Should Thiago Motta (who's been sensational this season) or Blaise Matuidi go down, it's panic stations. Likewise, Gregory van der Wiel is the only fit right-back and Thiago Silva is, for obvious reasons, irreplaceable.
Right now, it's smooth sailing for Real Madrid.
Under Jose Mourinho, there was always an underlying issue or two, and while the goalkeeping disturbance he created lives on under Carlo Ancelotti, los Blancos have hauled themselves right back into the Liga title contention over the past few weeks.
They've done well without Raphael Varane, Gareth Bale is becoming a force, Luka Modric is running the show and Jese is progressing. It's all too quiet!
Rudi Garcia is playing with fire at Roma, as his decision to send Nicolas Burdisso out on loan to Genoa is a very, very risky one.
Should Mehdi Benatia or Leandro Castan get injured or suspended, the Frenchman has only Alessio Romagnoli and Tin Jedvaj to call upon.
No one is doubting the immense potential both have—and Romagnoli has looked extremely assured whenever he's played—but they're challenging for the Serie A title and Champions League football. Is it wise to run with this group?