Chelsea have made some expensive transfer blunders down the years, with Ukrainian striker Andriy Shevchenko springing instantly to mind.
However, perhaps Chelsea’s biggest mistake was a signing they missed out on, rather than one they made?
According to The Mirror, the Blues were given the chance to sign French wonderkid Kylian Mbappe for just £17,000 four years ago.
Chelsea apparently decided against taking amateur club Bondy up on the offer, which looks like a ridiculous bargain with the benefit of hindsight.
Mbappe, who instead moved to Clairefontaine and is now at AS Monaco, is today worth around £100m, per The Mirror.
Eighteen-year-old Mbappe has scored 14 goals in 14 Ligue 1 starts and 11 sub appearances this season.
He has also netted five Champions League goals and could add to that tally when Monaco take on Juventus in the semi-finals tonight.
The Mirror claim that Chelsea’s decision not to sign Mbappe in 2013 was motivated by a desire to instead focus on the development of local prospects Dominic Solanke and Tammy Abraham.