5 most expensive defenders of all time
#4 Benjamin Mendy - July 2017 (Monaco - Manchester City) - €58.1m
The Frenchman had played a crucial role in Monaco's spectacular 2016/2017 season which saw them win the French League and make it all the way to the Champions League semi-final.
It was expected that he would provide width opposite Kyle Walker and his early form at City showed the shrewdness of the deal, with Mendy's pin-point delivery being a crucial part of Guardiola's attacking arsenal.
However, barely a month into the season, the World Cup winner damaged his right knee after a challenge with Crystal Palace's Andros Townsend, with scans showing he damaged his Anterior Cruciate Ligament which ruled him out for the next eight months.
He started the current campaign in impressive form, playing in 10 of City's first 12 league matches assisting five goals before once again suffering a long-term injury to his left knee. In total, Mendy has made just 18 appearances in all competitions for City and it is fair to say that he is a long way off repaying the huge fee paid to get him.