Chelsea overpaid by almost £40million when they signed goalkeeper Kepa Arrizabalaga from Athletic Club, according to CIES Football Observatory.
They also sold Thibaut Courtois to Real Madrid for £20million less than his value.
The first CIES Football Observatory Weekly Post of the 2018/19 season assesses from an economic perspective paid transfers having taken place during last summer. It highlights that Thibaut Courtois went to Real Madrid for a much lower amount than the estimated fair price (-€23 M) just as Chelsea FC paid over the odds to recruit his substitute: Kepa Arrizabalaga (+€45 M).
The best buy of the season was by Real Madrid, who purchased Thibaut Courtois from Chelsea for €40m, whereas his transfer value is closer to €62.6m.
The calculations worked out the ‘fair price’ as the average between the estimated cost for the most likely buyer before the transfer and the current transfer value.
Serie A is featured heavily in the best buys, as Cristante from Atalanta to Roma for €30m is the third best signing of the summer in Europe’s top five leagues, because his transfer value was quoted at €49.4m.
Radja Nainggolan from Roma to Inter for €40m was sixth in the list, with Cristiano Ronaldo eighth, because the price-tag of €105m was just shy of his actual transfer value of €116.5m.
Torino got a bargain with Simone Zaza for €14m from Valencia, compared to his €24.1m value, while Fiorentina got goalkeeper Alban Lafont for €8.5m and Toulouse could’ve commanded €18.4m.
Roma sold Alisson Becker to Liverpool for €72.5m, but that was still below his transfer valuation of €79.3m.
When it came to the worst buys, Alex Meret moved from Udinese to Napoli for €25m, a whopping €17.9m more than his transfer valuation.
Juventus also overpaid for Joao Cancelo to the tune of €17.7m, while Roma shelled out €17.1m too much for Javier Pastore from PSG.
At least Lazio made a tidy profit by selling Felipe Anderson to West Ham United for €37m, when CIES value him at €24.7m.