#3 AC Milan

To be fair, the AC Milan management made it clear late last year that there would be no major expenditure in the winter window. Nonetheless, it does feel like Milan have missed an opportunity this season.
With Juventus having a down year and Inter reeling from the loss of Antonio Conte and Romelu Lukaku, AC Milan had a real chance to push for league glory. Unfortunately, they have not been able to grab it and the current squad has gaping holes, especially in centre-midfield and at centre-back.
Reports suggest AC Milan made a strong push to sign Renato Sanches from Lille but the move eventually collapsed. Meanwhile, Juventus stunned the world by landing Dusan Vlahovic.
AC Milan are currently third, four points behind leaders Inter, who also have a game in hand. Their Champions League return didn't go as planned either as the club were eliminated in the group stage.
There is a sense that Ibrahimovic and co. don't have enough in the tank to challenge Inter and must be more wary of Atalanta and Juventus lurking right behind them.
#2 Manchester United

Just when it seemed like Manchester United were making progress under Ralf Rangnick, they were hit by the suspension and arrest of Mason Greenwood.
The Red Devils also sent out Anthony Martial, Donny van de Beek and Amad Diallo on loan. With four attacking players gone, United suddenly appear a bit lightweight, especially with Cristiano Ronaldo and Edinson Cavani in their twilight years.
The Red Devils' requirements are obvious - a defensive midfielder and a right winger. Unfortunately, Rangnick couldn't bring in any new players in the transfer window. The club also missed out on potential target Denis Zakaria, who joined Juventus instead.
Meanwhile, Jesse Lingard is still at the club, despite pushing very hard for a transfer. This means Manchester United are more likely than ever to lose him on a free transfer at the end of the season. It was a window filled with surprises, and not good ones.
#1 Arsenal

It felt as though over the course of the winter window, Arsenal and Tottenham Hotspur were locked in a mini-battle to see who could miss out on more targets. Spurs managed to avert embarrassment by landing Rodrigo Bentancur and Dejan Kulusevski from Juventus.
Arsenal, though, were able to offload Pierre-Emerick Aubameyang and his massive wages, bringing the Gabon forward's time in London to an end. Unfortunately, that's where the good news ends for the Gunners.
It means Mikel Arteta will go into the crucial second half of the season with very few options at centre-forward. The Gunners were linked with Dusan Vlahovic, Alexander Isak and even Alvaro Morata, yet somehow managed to miss out on all of them. With Alexandre Lacazette looking increasingly likely to leave the club, Arsenal desperately needed reinforcements up front.
The race for next season's Champions League qualification is heating up. Arsenal, Tottenham Hotspur, Manchester United and West Ham United are battling for fourth place, with Chelsea also threatening to drop into that mix. Arteta was completely justified in demanding new signings. The Spaniard will now have to make do without them.