With the January transfer window open, here's a look at the areas of greatest need for Europe's most celebrated clubs and title contenders:
Left-back: Dinamo Zagreb attacker Dani Olmo's move to Barcelona seems inevitable, and while the club is seeking a long-term Luis Suarez replacement, Inter's Lautaro Martinez won't be ready until June. We're making mountains out of molehills here, but Junior Firpo has not impressed at left-back.
Potential candidates: Alejandro Grimaldo (Benfica)
Backup CDM: Real Madrid's reliance on Casemiro will become apparent if the Brazilian gets hurt. The club is targeting Kylian Mbappe and Donny van de Beek in the summer, though immediate depth in defensive midfield wouldn't hurt. Rennes prodigy Eduardo Camavinga or Lille's Boubakary Soumare would provide cover with an eye to the future.
Potential candidates: Eduardo Camavinga (Rennes), Sandro Tonali (Brescia)
Striker: In Luuk de Jong, Chicharito, and Munir El Haddadi, Sevilla possess a full compliment of strikers who've underwhelmed. Quality over quantity should be a priority for a team that's challenging for La Liga honors, and last year's star striker, Wissam Ben Yedder, has not been adequately replaced.
Potential candidates: Michy Batshuayi (Chelsea), Krzysztof Piatek (Milan), Emmanuel Dennis (Club Bruges)
Striker: Atletico Madrid have scored the second-fewest goals in La Liga's top half, Diego Costa's run as a dependable and fit forward is done, and Diego Simeone tried to ship Angel Correa to Milan in a failed move. The backline was rebuilt in the summer; now it's time to do the same around Joao Felix.
Potential candidates: Rodrigo Moreno (Valencia), Paco Alcacer (Borussia Dortmund)
Forward: Maurizio Sarri has begun to experiment with a 4-3-1-2 that features Cristiano Ronaldo (34 years old) and Gonzalo Higuain (32) up top, but neither is getting any younger and Mario Mandzukic is gone, which perhaps explains why Juventus were in for BVB newboy Erling Haaland. However, they might have to wait until summer.
Potential candidates: Gabriel Barbosa (Flamengo), Victor Osimhen (Lille)
Midfielder: The gulf in talent between starters and bench could foil Inter's Scudetto chase. Marcelo Brozovic has been playing a lot and Stefano Sensi's repeated ailments signal the need for a box-to-box midfielder. Inter may be in the market for an attacking mid as well after missing out on Dejan Kulusevski.
Potential candidates: Arturo Vidal (Barcelona), Christian Eriksen (Tottenham)
Center-back: Mattia Caldara's uncertain return from a ruptured Achilles and a torn ACL paired with Leo Duarte's absence following ankle surgery means Milan could use some help in central defensive areas. With former Rossoneri fan favorite Thiago Silva available on a free transfer in the summer, Milan might wait.
Potential candidates: Jean-Clair Todibo (Barcelona), Thiago Silva (Paris Saint-Germain)
Everything: Napoli should be prepared for a slew of summer exits. Kalidou Koulibaly and Allan are both reportedly angling for a move, while Jose Callejon and Dries Mertens will be out of their contracts. Fabian Ruiz will also be a hot commodity following a career-defining campaign. Take your pick.
Potential candidates: Ricardo Rodriguez (Milan), Franck Kessie (Milan), Jan Vertonghen (Tottenham), Sander Berg (Genk), Andrea Cistana (Brescia)
Forward: Old man Edin Dzeko continues to lead Roma, but with depth at most other positions compared to scarce resources up top, it wouldn't hurt to acquire another central forward. Reported interest in Napoli's Mertens and Real's Mariano Diaz were shelved over wage demands.
Potential candidates: Michy Batshuayi (Chelsea), Andrea Pinamonti (Genoa), Krzysztof Piatek (Milan)
Center-back: One of Europe's surprise packages this season, Scudetto challengers Lazio are reportedly looking to bolster their defense in the summer, especially if Braga make Wallace's loan permanent. The goalposts may have shifted amid a shock title run, fueling January ambitions.
Potential candidates: Eray Comert (FC Basel), Rodrigo Caio (Flamengo)
Right-back: Bayern Munich's desire to shift Joshua Kimmich into a full-time midfield role would necessitate the addition of a full-back who could provide cover for Benjamin Pavard and allow the Frenchman to continue deputizing at center-back as Jerome Boateng's exit looms.
Potential candidates: Lukas Klosterman (RB Leipzig), Benjamin Henrichs (Monaco)
Midfielder: Borussia Dortmund's needs aren't that pressing, but after shipping Julian Weigl to Benfica, recruiting an extra deep-lying midfielder couldn't hurt. Juventus will be desperate to dump Emre Can, although a more long-term, defensively minded midfielder might be a better fit.
Potential candidates: Emre Can (Juventus), Marc Roca (Espanyol), Tomas Soucek (Slavia Prague)
Full-back: Bayern's hunt for Klostermann could see Leipzig's public pursuit of Monaco's Henrichs come to fruition. Heinrich can play both full-back positions and as a No. 6. Leipzig might also fancy replacements for summer migrators Dayot Upamecano and Timo Werner.
Potential candidate: Benjamin Henrichs (Monaco), Gonzalo Montiels (River Plate)
Central midfielder: Surprise side Borussia Monchengladbach have relatively modest means, and as such, they will likely sell Denis Zakaria in the summer. In-house options exist in Tobias Strobl and Laszlo Benes, though the latter has been a revelation this season in more of an attacking role.
Potential candidates: Sander Berge (Genk), Teun Koopmeiners (AZ Alkmaar)
Full-back: Central midfielders Emre Can and Allan (Napoli) have been linked with a move to the French capital, though reinforcements at either full-back position are more necessary for PSG. Thomas Meunier (RB) continues to underwhelm, and Layvin Kurzawa (LB) will be out of contract in the summer.
Potential candidates: Mattia De Sciglio (Juventus), Joao Cancelo (Manchester City)
Striker: Marseille have been a pleasant surprise under Andre Villas-Boas. Still, they could look to move on from out-of-form striker Valere Germain, on-loaned Kostas Mitroglou (PSV), and winger Saif-Eddine Khaoui. Dario Benedetto could use cover - whether for the short term or the long haul.
Potential candidates: Boulaye Dia (Reims), Daniel Sturridge (Trabzonspor)
Attacker: Long-term injuries to Jeff Reine-Adelaide and Memphis Depay have swiftly altered Lyon's plans, and there's a chance that Les Gones will sell Moussa Dembele (FW) and Lucas Tousart (MF). Still, the absence of Reine-Adelaide's ball progression and Depay's goal involvement needs addressing.
Potential candidates: Thomas Lemar (Atletico Madrid), Gedson Fernandes (Sporting)