Liverpool secured the best bargain of the summer transfer window from a financial standpoint with their impressive capture of former Chelsea winger Mohamed Salah from AS Roma, according to the latest two-part monthly report from the CIES Football Observatory in Neuchatel, Switzerland.
Using an algorithm that calculates the gap between a player's scientifically estimated value and the fee they were eventually signed for, the study claims that €69.4m-rated (£63.5m, $82.5m) Salah was sold for €19.4m less than he should have been in a then club-record deal that could eventually be worth as much as €50m with add-ons.
Next on the list is former Manchester City winger Nolito, who returned to La Liga with Sevilla in July for a reported €10m fee - €17.4m less than his calculated value.
AS Roma could seemingly also have demanded €15.2m more than the €39m they received from Chelsea for German international defender Antonio Rudiger.
By contrast, Kylian Mbappe's controversial exit from AS Monaco is rated as the most overpaid transfer. The teenage wonderkid joined Ligue 1 rivals Paris Saint-Germain on an initial season-long loan that includes the option to make the arrangement permanent next summer at a significant cost of €180m.
Ambitious Everton's deals for goalkeeper Jordan Pickford and Icelandic playmaker Gylfi Sigurdsson both feature in the top five, behind new Barcelona recruit Ousmane Dembele and new City left-back Benjamin Mendy.
Crystal Palace and Manchester United are said to have overpaid by €22.9m and €20.1m for Mamadou Sakho and Nemanja Matic respectively. Leicester City's Harry Maguire, Chelsea deadline day arrival Davide Zappacosta, City defender Kyle Walker and Liverpool newcomer Alex Oxlade-Chamberlain can also be found inside the top 20 of biggest discrepancies along with Patrik Schick, Dalbert Henrique, Anthony Modeste, Leandro Paredes, Milan Skriniar and Keita Balde Diao.
On average, CIES report that European clubs overpaid on transfers by approximately 30% in a year that outfits from the top-five strongest leagues - Premier League, Bundesliga, La Liga, Serie A and Ligue 1 - set a fifth successive new record by lavishing an eye-watering €5.9bn on new signings. The €5.1bn spent in the summer alone was a 38% increase on the €3.7bn that changed hands during the same period in 2016.
It is additionally stated that Premier League sides spent €1.55bn in up-front transfer fees and a further €220m in potential add-ons at an average of €89m per club. Swansea City and Arsenal feature in a top 10 of positive balance sheets predictably headed by Monaco, while United, City, Chelsea and newly-promoted duo Brighton & Hove Albion and Huddersfield Town all make the corresponding list for negative balances behind big-spending PSG and AC Milan.