The most important time of the season for some clubs is the transfer window, this allows them to sell players, but more importantly to them and their fans, buy players.

By having a successful transfer window clubs can lay the groundwork for a successful season and seasons to come, but an unsuccessful window can set a club back many years, and cause millions of pounds to be wasted.

In this list, we will look at some of the worst transfer windows ever conducted by clubs.

5 Liverpool – 2010

American businessmen Tom Hicks and George Gillett purchased Liverpool in February 2007 and provided the Reds fans with some of the worst seasons in the club's recent history.

This came to a head in the 2010 summer transfer window, where they signed eight players for a total expenditure of €30.23m, despite earning €36m in revenue from player sales, including the sale of world-class midfielder Javier Mascherano to Barcelona for €20m, per Transfermarkt.

To replace Mascherano, new manager Roy Hodgson brought in the headline signings of Joe Cole and Milan Jovanovic, who were both signed on free transfers, however, between them, they only made 60 appearances and scored seven goals in their time with the club.

Their most expensive signing of the window was a 27-year-old Portuguese midfielder Raul Meireles, who signed for €13m from Porto, but only a year later Meireles was sold to Chelsea for €500k more than he was bought for.

Unsurprisingly Liverpool finished the year in sixth position with 58 points, leading to owners Hicks and Gillet selling the club in October 2010, a month and a half after the transfer window shut.

4 Chelsea - 2017

Antonio Conte’s Chelsea had just come off the back of a very successful 2016/17 campaign that saw them win the league by seven points.

However, at the end of the season clinical striker Diego Costa left the club and returned to Atletico Madrid for €60m, leaving Chelsea without a striker for the upcoming season.

This led The Blues to sign 24-year-old Spanish striker Alvaro Morata from Real Madrid for €66m, making him Chelsea’s most expensive signing at the time.

Despite this, Morata’s move to Chelsea turned out to be one of the biggest transfer flops ever, the striker only played 72 times across two seasons for The Blues, scoring 24 goals and recording six assists in all competitions, before he moved to Atletico Madrid, per Transfermarkt.

Morata wasn’t the only big-money signing that failed for Chelsea that summer, Danny Drinkwater signed from Leicester for €37.9m and only went on to play 23 times for the London outfit before leaving on a free transfer.

Alongside Drinkwater Chelsea also signed the French defensive midfielder Tiemoué Bakayoko from Monaco for €40m, Similar to Drinkwater Bakayoko only played 43 times before leaving Chelsea.

The blue side of London also signed Antonio Rudiger and Davide Zappacosta, who have both left the club as well, meaning that none of the players signed in this window are still there, despite spending €194.6m.

Furthermore, in the season that followed Antonio Conte lost his job and Chelsea finished fifth, 23 points worse off than the year before.

3 Manchester United – 2009

Despite not spending as much as Chelsea in this transfer window the players they signed compared to the players they sold has to go down in history as one of the worst transfer windows.

United had won the previous three League titles, a record for Sir Alex Ferguson, and reached the Champions League final only to be beaten by Barcelona, however, they lost their talismanic figure Cristiano Ronaldo to Real Madrid for €94m.

This left Manchester United needing serious reinforcements to cover the 38 goal contributions that Ronaldo provided and to do this they only brought in four players that cost €27.3m in total.

The highlight of these was Micheal Owen who signed on a free transfer from Newcastle who were in the Championship, per Transfermarkt.

Alongside Owen, they also signed Antonio Valencia (who did go on to have a solid career at the Red Devils, even captaining the side), Mame Diouf and Gabriel Obertan.

Unsurprisingly to some Manchester United fans, they were unable to retain the league title that year, losing out by one point to Chelsea.

2 AC Milan – 2017

Before the 2017/18 season, the once-great AC Milan had finished outside the top five for the fourth season in a row, and in 2016/17 they 23 points off Champions League Qualification, to try and counter this the club signed 11 new players (none of whom are at the club now).

The 11 players brought in cost the Rossoneri £221.8m, while the 14 players that were sold only brought in £22.4m, per btl

The two statement signings of the transfer window by new owner Li Yonghong were Lionardo Bonnucci and Andre Silva, who joined for a combined fee of £72m, and have both since left the club for a combined fee of £38m, meaning Yonghong, made a loss of £34M on those players alone.

Despite the excessive spending and lots of players, Milan was still only able to finish sixth in the table 31 points off first place Juventus.

Following Yonghon’s excessive spending Milan broke FFP regulations and were banned from all European competions, following this in 2018 Yonghong sold AC Milan.

It would take until the 2020/21 season for Milan to regroup and make it back into the Champions League spots, after they finished second in the league.

1 Chelsea – 2022

Maybe unsurprisingly to some, Chelsea have made their second appearance on this list, but this time it is for a much more recent transfer window.

In May 2022 Todd Boehly bought Chelsea for £4.25bn, and since then he has certainly been putting his money where his mouth is, spending nearly £1bn across three transfer windows, with the first of these being one of the worst in history.

Boehly bought eight different players during the window including Wesley Fofana, Marc Cucurella, Raheem Sterling, Kalidou Koulibaly, Careny Chukwuemeka, Pierre-Emerik Aubameyang, Gabriel Slonina and Denis Zakaria, costing £281.99m, per Transfermarkt.

However, since signing these players only a year ago only Sterling and Cucurella are available for selection, as the remaining six have either left the club, gone out on loan, or their loan wasn’t renewed.

Wesley Fofana was the most expensive transfer that summer, costing €80.4m, but since signing he has only played 20 times for the Blues, summing up what was a really poor summer for them.