Jurgen Klopp's Liverpool had a roller coaster of a 2020-21 season across all fronts.The Reds had a superb start to the campaign as they looked to defend their first Premier League crown in 30 years. While they were once atop the Premier League standings, their season quickly began to unravel in a dramatic fashion. The biggest talking point of their season was the astonishing number of injuries they faced, particularly in defence.Superstar defender Virgil van Dijk was on the end of an ill-advised tackle from Jordan Pickford in a heated Merseyside derby back in October. This led to him being ruled out for the season. Joe Gomez joined him on the treatment table as he too was ruled out of the season after a serious knee injury (patellar tendon rupture) with England in November.Liverpool’s injuries in the Premier League this season:Van Dijk (33 games missed)Gomez (31)Matip (28)Keita (28)Jota (19)Henderson (17)Thiago (14)Fabinho (8)Still finished third. 😤 pic.twitter.com/Z7IXDr9r2F— B/R Football (@brfootball) May 23, 2021With Joel Matip also injured, Liverpool were forced to rely upon rookie defenders Nat Phillips and Rhys Williams for large parts of the season. The two young defenders were partnered by the likes of Fabinho, Jordan Henderson, and winter loan signing Ozan Kabak. In total, Liverpool have fielded an astonishing 21 (!) different league combinations this season.Given their miserable injury situation, it's quite a remarkable feat for Klopp's men to finish in their place in the Premier League. Liverpool evidently want to be better prepared for a similar situation in the future and have begun to make moves in the transfer market.The Reds sealed the signature of one of Europe's most exciting talents, Ibrahima Konate, in a €40m deal. Here, we take a look at where Konate ranks among Liverpool's most expensive defenders of all time.Liverpool's most expensive defensive signings#5 Mamadou Sakho | €19mLiverpool FC v Crystal Palace - Premier LeagueFrench defender Mamadou Sakho was a popular cult figure at the club during his time in Merseyside. A no-nonsense centre-half by trade, the towering Frenchman moved to Liverpool in the summer of 2013 for a fee of €19m. He left his boyhood Paris Saint-Germain after 201 appearances in all competitions.Sakho was part of Brendan Rodgers' squad that nearly won the title back in 2013/14. However, the 31-year-old's role at the club began to reduce in the following seasons before a permanent move to Crystal Palace four years later. The former PSG captain made 80 appearances on all fronts for the Reds' senior side.Special visit at Melwood this morning !! 👍🏿 - Ce matin à Melwood ! #YNWA #LFC pic.twitter.com/buho4yCb5q— Mamadou Sakho (@mamadousakho) March 8, 2016In many ways, he's had an unfortunate career. Neither did he manage to stay at PSG for their golden era of French domination, nor did he witness the immense success that Klopp brought about.#4 Glen Johnson | €20.5mChelsea v Liverpool - Premier LeagueFormer England international Glen Johnson moved to Liverpool back in 2009 on the back of a superb spell with Portsmouth. The right-back joined the Reds in a deal worth up to €20.5m, making him their most defensive signing at the time. He is the oldest transfer to make it to this list, and the only one made in the 2000s.Johnson was one of Liverpool's most consistent performers during his spell at Anfield. The former Chelsea man ended up making 200 appearances for Liverpool across all competitions, scoring nine goals and setting up 19. Johnson helped the Reds win the 2011-12 EFL Cup before moving to Stoke City on a free transfer.Also read: 5 Most valuable Spanish players in Europe