Liverpool's £75-million swoop for Virgil van Dijk set an early benchmark for what could be the costliest January window of all time. A host of players with equal or greater pedigree are already on the brink of making big-money moves abroad.
The following rumours will demand everyone's attention over the next few weeks:
It's the worst-kept secret in football. Everyone knows Barcelona wants Philippe Coutinho, and vice-versa. The question is whether Liverpool will sanction the player's departure, and how much money it would take to convince the Reds.
Liverpool owners Fenway Sports Group resisted three lucrative bids last summer, and although Barcelona has yet to officially lodge a fourth, it appears FSG is inclined to accept an offer worth more than £130 million.
For his part, Coutinho has produced some of the best football of his career. He's contributed to 20 goals in 19 appearances this season, helping Liverpool reach the knockout stage of the Champions League.
Barcelona has also done pretty well in the time since, surging to the top of the La Liga standings while going the past 25 matches unbeaten. Adding to the good vibes is the prospect of Ousmane Dembele returning from a serious hamstring injury.
Barcelona doesn't appear to be so desperate for recruitments anymore. Will that affect negotiations for Coutinho?
The next-best thing in football is Sergej Milinkovic-Savic. Already piped to join Paris Saint-Germain for a reported €170-million fee, the Serbian midfielder has the creative instincts and explosiveness that every manager covets.
He's carved a nice spot for himself at Lazio, boosting the side to fifth place in the Serie A standings last season. Never shy to dash through the pitch and take a long shot at goal, Milinkovic-Savic has decided the outcome of several matches in the Italian top flight.
Considering PSG is already tip-toeing the limits of UEFA's Financial Fair Play regulations, it would likely have to sell players before moving for Milinkovic-Savic. Manchester United is also rumoured to be interested.
Wherever he ends up, Milinkovic-Savic will bring an energetic presence to the pitch.
But in the intervening months, Sandro has looked like anything but the enterprising full-back he was last season. Manager Massimiliano Allegri dropped the Brazilian in key matches against Napoli and Inter, and club CEO Giuseppe Marotta has said he will sell any unhappy player.
It's still a bit of a surprise that Chelsea has reignited interest in Sandro, with a £50-million bid reportedly on the table. Marcos Alonso is thriving at the left wing-back position, scoring his sixth Premier League goal on Wednesday against Arsenal. But Sandro would answer Antonio Conte's calls for a bigger squad. A move could also provide the slumping Sandro with a necessary boost ahead of the World Cup.
Arsene Wenger has done all he can to keep Alexis Sanchez in north London, but the temperamental Chilean is as unlikely to sign a new contract with the Gunners as he's ever been.
Critics have picked apart his body language and accused the player of quitting on the team, while reports of a rift in the dressing room have emerged again.
Considering FIFA allows players in the final six months of their contract to speak to different clubs, Sanchez can freely test the waters. However, prospective suitors may feel they'll lose out on the 29-year-old if they don't act right away. Arsenal may too be ready to cash in on a player who could leave the club for free next summer.
Now that Gabriel Jesus is out for at least a month of action, it's possible manager Pep Guardiola will ask Manchester City to revive negotiations for Sanchez. City tried to draft in the Copa America winner on the final day of the summer transfer window, only for Arsenal to block the deal in the 11th hour. Coutinho's situation at Liverpool, meanwhile, could force the Reds into a bidding war.
A dominant showing in the Confederations Cup thrust Leon Goretzka in the spotlight. Leading the tournament with three goals, he put on display his box-to-box prowess. And so the race for his signature began as he entered the final year of his contract with Schalke.
Bayern Munich - which has a habit of cherry-picking the Bundesliga's best players - has already confirmed its interest in Goretzka. Should the 22-year-old make the switch to Bavaria, he would join a long list of talent to arrive for chump change; Robert Lewandowski, Joshua Kimmich, and Sebastian Rudy all cost less than €10 million. Bayern would only add to its impressive track record by signing Goretzka on a free transfer.