Kylian Mbappe was most overpriced signing of summer transfer window but Mohamed Salah was excellent value for money, according to study

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Paris Saint-Germain overspent on Kylian Mbappe by more than €87million, according to a study by the CIES Football Observatory.

The French youngster commanded a whopping €180m fee (to be paid next year) when he made the switch from Monaco to Paris Saint-Germain last month, making him the second most expensive footballer of all time at the age of 18.

But the Ligue 1 giants may have splashed out considerably over the odds, if the CIES 'transfer value calculator' is anything to go by.

Paris Saint-Germain signing Kylian Mbappe was the most overpriced of the summer window

The French international cost more than €87m more than a study's estimated transfer value

The widget, which takes a series of data entries relating to a player's age, position, domestic and international performance and contract length and churns out a price tag, rated Mbappe at €92.6m, way down on what PSG paid.

The discrepancy between his estimated value and true worth was €36m larger than any other player's, with Ousmane Dembele second on the list following his move to Barcelona from Borussia Dortmund.

Of the top 20 transfers where the projected price tag was most different to the amount shelled out, only three were suggested to have been value for money.

Liverpool's acquisition of Mohamed Salah topped that list. The Egyptian had an estimated value of €69.4m and an actual cost of €50m, while a surprise entry was Spanish striker Nolito.

The forward, who had struggled at the Etihad Stadium, secured a transfer to Sevilla for €10m despite holding a dubious estimated value of €27.4m.

Liverpool's Mohamed Salah was the best value for money on offer during the window

In the study, which covered the top five leagues in Europe, the Football Observatory announced that it expected spending to continue to rise over the next half a decade while also warning about the need for clubs to diversify in an effort to sustain revenue streams as and when the TV rights deals fall into decline.

It revealed that Premier League clubs created a €835m transfer deficit in the recent transfer window, while spending across big five leagues increased for the fifth successive year.

Summer spending of €3.7billion in 2016 jumped up 38 per cent to €5.1b this time around.

Interestingly, La Liga ended the window with a €9m surplus.

That would undoubtedly have been aided by Real Madrid finishing €47m in the black and Atletico Madrid finding themselves under a UEFA transfer ban.

In general, Spanish clubs' average outlay in the summer window was €34m, trailing Serie A (€55m) and way behind the Premier League.

On average, teams in England spent €89m each on new players.