1. Kyle Walker - £50m
City splurged more than £100m on new full-backs in the summer of 2017, with the former Spurs man being the second full back arrival of Pep's record-breaking campaign. Having grown into the Premier League's best right-back under Mauricio Pochettino at Spurs, Kyle Walker upped his game, even more, at City. He quickly established himself as a key component of Pep's defence, winning two Carabao Cup titles and the Premier League to date.
2. Benjamin Mendy - £52m
Pep Guardiola broke the record for a defender when he signed Mendy from Monaco on July 2017. The transfer fee eclipsed the previous record for a defender, set 10 days prior by City on teammate Kyle Walker. An enigmatic and eccentric character off the field, the left-back rose to prominence as one of Europe's most exciting full-backs in the 2016-17 season as Monaco won Ligue 1 - while also reaching the Champions League semi-finals. Although he is yet to live up to the £52m fee in City colours as countless injury problems have seriously hindered his progression.
3. Aymeric Laporte- £57.2m
This could look like a list of only Manchester City players but it is not. Guardiola after spending around £200m in the Summer again went for defensive recruitment in January and Laporte has since then become City's defensive linchpin, being the first name on the team-sheet.
4. Virgil van Dijk - £75m
Arguably the best defender right now. Liverpool missed out on signing him in the summer of 2017 but ultimately signed him for a world record fee which surely has turned out to be the right decision. He has looked worth every penny since making the switch to Anfield, winning the Professional Footballers' Association Players' Player of the Year last term and helping the club clinch its sixth Champions League title.
5. Harry Maguire- £80m
Manchester United's search for a defensive recruit finally become fruitful this week when they signed Harry Maguire from Leicester. However, to achieve the target they have had to break the bank with a world record fee of £80m.
The transfer capped quite a rise for the defender, who joined Leicester from Hull City in 2017 for £15m and went on to make 76 appearances for the club. United was desperate for a player to strengthen the heart of their defence and only time will tell if he's worth it or not.