So far, Liverpool have been the only club to make a significant move by completing the £7.25m deal for FC Salzburg attacking midfielder/forward Takumi Minamino. Yet with the race for trophies and Champions League qualification taking shape, a January signing could prove transformative for some clubs.
Liverpool remain on course to win the Premier League title and retain the Champions League while Leicester, Manchester City and Chelsea are sitting pretty in the European positions. Manchester United, Tottenham and Arsenal still have ground to make up, so what should the top clubs be targeting first to make a difference this month?
Liverpool were smart and decisive to wrap up the Minamino deal ahead of the transfer window. The Japan forward, who made his debut in the FA Cup win against Everton, adds attacking quality and depth to Jurgen Klopp's squad, while they got him at a bargain price by triggering his £7.25m release clause at FC Salzburg.
Considering Liverpool are 13 points clear at the top of the Premier League, there would be little value in the club making more signings this month. 'If it isn't broken, don't fix it,' would be the obvious mantra at Anfield.
LEICESTER: A proven striker
Brendan Rodgers has exceeded all expectations at the King Power Stadium by putting Leicester on course for a return to the Champions League, four years on from the club's unforgettable Premier League title-winning campaign. With a 14-point cushion between them in second and Manchester United in fifth, Leicester are well-placed to clinch Champions League qualification. But a quick look at their stats this season highlights the big weakness that could see it all unravel if Jamie Vardy gets injured.
The former England striker has hit 17 goals in 19 league games so far this season, but Leicester have no other player who has reached double figures, with their next highest scorer being midfielder James Maddison (six). If Vardy stays fit, Leicester will cruise into the Champions League, but signing a proven striker this month would give them a much-needed insurance policy.
MAN CITY: A central defender
Manchester City sit 14 points behind Liverpool, having played one more game, and much of that can be put down to the defensive problems that have plagued the defending champions all season. Pep Guardiola wanted a new centre-back to fill the gap left by Vincent Kompany's departure to Anderlecht last summer, but with City unable to sign a foreign defender (due to having already filled its quota of non-British players), he was left with limited options and one of them, Harry Maguire, ended up becoming the world's most expensive defender when he joined Manchester United from Leicester for £85m. Aymeric Laporte's knee ligament injury in August then proved disastrous, leaving Guardiola without the defensive pairing which guided City to the title.
Despite Laporte being close to a return to action this month, the unreliability of John Stones and Nicolas Otamendi has made a new centre-back a must this month. Once again there are few obvious options, but City have the money to find the right man.
CHELSEA: A box-to-box midfielder
N'Golo Kante is arguably the best defensive midfielder in the world, the France international boasting much more to his game than destructive qualities, but Chelsea are still too lightweight in the heart of the pitch. Manager Frank Lampard has money to spend this month following the lifting of Chelsea's two-window transfer ban and he needs reinforcements in every department to add experience to the club's emerging young stars. But if he can find a younger version of himself -- a box-to-box goal scoring midfielder -- Lampard would potentially spend all of his budget on that crucial addition to his squad.
A player like Man City star Kevin De Bruyne would be the perfect foil for Kante, but that is a sore subject at Chelsea considering that they let the Belgian midfielder leave earlier in his career.
MAN UNITED: A quality midfielder
The easy answer would be to suggest that Manchester United need help all over the pitch because of the state of Ole Gunnar Solskjaer's side. Injuries and loss of form are biting hard into what was already a weak squad populated by too many young and inexperienced players. But while United do need reinforcements in every position, the most pressing area is midfield. Even with a fit Paul Pogba -- and that has been a rarity this season -- United lack quality and depth in midfield. But if they find an experienced midfielder capable of bringing maturity, energy, organisation, creativity and goals to the team, it could be the difference between a top-four finish and missing out.
United basically need a modern-day version of Roy Keane, but it may need three players to do the job of one. If they can seal a deal for Ajax's Donny van de Beek, as sources told ESPN they are trying to, they would at least solve the problem of goals, energy and creativity.
TOTTENHAM: A backup striker
Harry Kane's hamstring injury, which will keep the England striker out until April, has made it even more important for Spurs to sign a striker this month. But attacking reinforcements were needed even before Kane succumbed to his latest setback.
Spurs have shown in the past that they are capable of winning games without their talisman -- they qualified for last season's Champions League final despite Kane being injured for the final two months of the campaign -- but, as Jose Mourinho pointed out this week, neither Lucas Moura nor Son Heung-Min are strikers in the true sense, even though they both have the ability to score goals.
Signing another striker would give Mourinho and Spurs a much-needed option, but crucially he would also enable Kane to be rested more often in the future. The 26-year-old rarely sits games out, but he also spends too much time on the sidelines because of injury. A striker to share the burden of games and goals would help everybody at Tottenham.
ARSENAL: A reliable defender
Mikel Arteta is enjoying a bounce as Arsenal's new manager after failing to win his first three games in charge, but he faces a difficult challenge to sustain the feelgood factor and improved results. He should be able to rely on Alexandre Lacazette and Pierre-Emerick Aubameyang to continue to score goals and in midfield, Arsenal are showing signs of being a harder working, more cohesive unit than under Unai Emery.
But Arsenal still look unconvincing at the back and Arteta needs to find at least one reliable defender this window after the season-ending injury to Calum Chambers. David Luiz is always one game away from a defensive catastrophe, while Sokratis is not quick enough to cope with the Premier League. Rob Holding remains a good prospect, but Arsenal need a centre-back they can rely on to be fit and influential. And they don't have that right now.