An analytical report by The CIES Football Observatory over summer spending by European clubs indicated that Mohamed Salah's move to Liverpool was the best bargain in the transfer window.
The data-driven analysis, which uses various statistics to calculate a value for a player, set the estimated value of the in-form Egypt winger at 69.4m euros.
Liverpool had paid AS Roma a 50m euro club record fee to land Salah but the study suggests that this figure is well below his true worth.
"According to the algorithm developed, the most over-paid transfer in absolute terms was that of Kylian Mbappé from Monaco to Paris St-Germain: +€87.4 million between the amount reported (add-ons included) and the estimated sum," the study said.
"Conversely, the best bargain from a financial point of view was achieved by Liverpool for the recruitment of Mohammed Salah (-€19.4 million)."
Salah made an explosive start with Liverpool, scoring three goals in five competitive appearances - two in the Premier League and one in the UEFA Champions League playoff.
The 25-year-old scored the goal which led Egypt to a crucial 1-0 World Cup qualifying win at home to Uganda on Tuesday as they seek to qualify for the most prestigious football showpiece for the first time since 1990.
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