Athletic Bilbao coining it with "clause or nothing" approach
The release-clause sales of Kepa Arrizabalaga, Aymeric Laporte, Ander Herrera and Javi Martínez have netted The Lions €221 million in recent years.
Kepa Arrizabalaga's world-record move to Chelsea made him the latest player to rake in a huge transfer bounty for Athletic Bilbao.
The LaLiga club's unique policy of only signing players hailing from the Basque region informs a policy of inserting substantial release clauses into the contracts of their prized assets.
Under the presidency of Josu Urrutia, the so-called "clause or nothing" approach has seen four players sold for the terms outlined in their contracts – netting Athletic a massive €221 million.
Javi Martínez - €40m to Bayern Munich (August 2012)
A deal that made the Spain international the most expensive purchase in Bundesliga history. Comfortable in either holding midfield or the centre of defence, Martínez won the Champions League in his first season with Bayern and has collected six consecutive Bundesliga titles, although persistent injury problems have plagued his time in Bavaria.
Ander Herrera - €36m to Manchester United (July 2014)
A year after David Moyes launched a failed bid for Herrera, United got their man amid the transfer splurge that began the Louis van Gaal era. Technically assured and with a combative streak that makes him a favourite of José Mourinho, United's best performances tend to coincide with when the 28-year-old is on top form.
Aymeric Laporte - €65m to Manchester City (January 2018)
An elegant, ball-playing defender naturally attuned to Pep Guardiola's style, Laporte became City's record signing earlier this year. He has since lost that status to Riyad Mahrez but the imposing Frenchman – whose progress through the youth ranks at San Mamés made him eligible for the first team – is well placed to established himself as City's first-choice centre-back this season, having already pocketed a Premier League winners' medal.
Kepa Arrizabalaga - €80m to Chelsea (August 2018)
Kepa made the Athletic number-one spot his own after returning from a loan spell with Real Valladolid at the start of the 2016-17 campaign. His form caught Real Madrid's attention but mounting transfer speculation culminated in him signing a seven-and-a-half-year contract extension at San Mames in January. That deal contained the clause that forced Chelsea to make the 23-year-old the most expensive goalkeeper of all time.