Teams including Real Madrid and Bayern Munich might move for players to boost their title hopes, with both sides currently adrift in their respective races.
Premier League clubs are typically the biggest spending in the world and, with Liverpool's title charge looking ominous, chequebooks may open at Manchester City and Tottenham in a bid to stop the Reds.
But what do each of Europe's elite clubs really need to do in the transfer window?
Liverpool
The league leaders have a strong squad but more cover may be needed, particularly if squad players like Alberto Moreno and Simon Mignolet depart. Midfielder Alex Oxlade-Chamberlain's return is likely to provide a timely and potentially crucial late-season boost.
Manchester City
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Defeats to Crystal Palace and Leicester City without Fernandinho highlighted the Brazilian's importance to the champions. He is 33 and a successor must be a high priority for Manchester City, who have used Ilkay Gundogan and John Stones in that role with little success, having missed out on Jorginho to Chelsea.
City also have a problem position at left-back, where a succession of injuries to Benjamin Mendy have repeatedly left Pep Guardiola using square pegs to fill a round hole.
Tottenham
Spurs infamously signed nobody in the last transfer window but it doesn't appear to have harmed Mauricio Pochettino's side. Injuries have since affected his midfield options, however, and a mooted move for Adrien Rabiot – who has made no secret of his desire to leave Paris Saint-Germain – makes plenty of sense on paper. Unfortunately for Spurs, the latest stories suggest that the Frenchman is setting his sights higher.
The future of Toby Alderweireld remains a question mark, although diligent work has been done securing the futures of many other key players, such as England stars Harry Kane and Dele Alli.
Arsenal
Defensive injuries have hit Unai Emery's squad and a strong centre-back would be a useful addition in January. With Aaron Ramsey set to leave at the end of his contract, Arsenal also need to replace the Wales midfielder and Sevilla star Ever Banega has been linked as a possible signing.
Emery may also be tempted to entertain offers for former Germany playmaker Mesut Ozil, given he has been on the fringes despite pocketing a reported £350,000 a week.
Chelsea
A striker is top of the wish list for Maurizio Sarri, who has selected Eden Hazard as a false nine ahead of Alvaro Morata and Olivier Giroud - who joined last January. Interest in Bournemouth's Callum Wilson has been confirmed by Sarri's assistant Gianfranco Zola, with Jamie Vardy and Gonzalo Higuain among the other names linked.
Another month of speculation over Hazard's future seems certain, with the Belgium star's deal set to expire in 2020.
1 - Callum Wilson is the first ever @afcbournemouth player to score for @England, and the first player to score on his Three Lions debut since Marcus Rashford in May 2016. Beginnings. #ENGUSA— OptaJoe (@OptaJoe) November 15, 2018
Manchester United
United may opt not to invest with caretaker boss Ole Gunnar Solskjaer only technically in charge until the end of the season. Jose Mourinho wanted defensive reinforcements and this still seems the most obvious area of improvement in United's squad, along with more dynamism in central midfield, but the club's hierarchy have reportedly told Solskjaer that he will only be allowed to sign players on loan. Is Henrik Larsson still kicking about?
SEE ALSO Henrik Larsson at Manchester United: how a 10-week loanee made a major impact at Old Trafford
Barcelona
Jeison Murillo has joined on loan from Valencia to address a defensive injury crisis, with head coach Ernesto Valverde intimating that La Liga's leaders will not be pursuing further signings in January. Philippe Coutinho has been out of the side, though, and he could be sold to raise funds if there was interest. Reports of a possible swap-deal with PSG involving Coutinho and Kylian Mbappe appear far-fetched, though.
Real Madrid
Madrid haven't spent big money for a few years, and there should also be cash left over from Cristiano Ronaldo's €105 million move to Juventus. Whether the club are willing to back Santiago Solari, who feels like a stopgap appointment, remains to be seen.
Ronaldo's goals are much missed and a forward to relieve the burden on a misfiring Karim Benzema would presumably be a priority. Ballon d'Or winner Luka Modric may again be the subject of transfer talk, having been linked to Inter Milan before the season started.
Atletico Madrid
Diego Simeone splashed his cash in the last window, signing Thomas Lemar, Rodrigo, Nikola Kalinic and Gelson Martins to join his side's title push. But Atletico face a battle to hold on to World Cup-winning defender Lucas Hernandez, with Bayern Munich ready to trigger his release clause according to reports in Spain. Replacing Lucas would be tough and the advancing age of captain Diego Godin, 32, may be on Simeone's mind, as well as a lack of goals from Diego Costa.
PSG
It's unclear whether there's any money available for Thomas Tuchel, but the signing of Eric-Maxim Choupo-Moting from Stoke in the last window suggests budgets have been tightened after years of lavish spending in the French capital. Speculation will surround Neymar and Kylian Mbappe while another midfielder will be needed if Rabiot gets his desired move away - Barcelona have made little secret of their admiration. Watford's Abdoulaye Doucoure is reportedly a target.
Bayern Munich
With six points to make up on Bundesliga leaders Borussia Dortmund, Bayern may opt to splash the cash. The club have confirmed interest in Lucas, for whom a deal would smash their surprisingly modest transfer record. Reinforcements are also required in attack with Arjen Robben leaving at the end of the season, Franck Ribery expected to follow suit, and Kingsley Coman plagued by injuries.
Juventus
On track for yet another Serie A title, Juve have no obvious weaknesses and they spent big in the last window to land Ronaldo from Madrid – a deal that appeared a clear attempt to boost their chances of winning the Champions League. Vastly experienced defenders including Giorgio Chiellini, 34, will need replacing at some point... but probably not now.
Inter Milan
Inter head coach Luciano Spalletti will also be hoping for additions during the transfer window. Keeping club captain Mauro Icardi - previously linked with Madrid - is a must, but more firepower is needed to alleviate the heavy burden on the Argentina attacker's shoulders.
Gennaro Gattuso's side have also been struggling for goals despite landing Higuain on loan from Juve - his winner in Saturday's 2-1 defeat of SPAL was his first goal since October. It is possible that Higuain leaves, which would mean at least one attacker needs to be signed, although Patrick Cutrone has plenty of promise and deserves more opportunities. Sevilla's out-of-favour Luis Muriel has been linked, but whether any signings come under Gattuso - who is under increasing pressure - remains to be seen.
