Mundo Deportivo have claimed that between September 2009 and October 2010, the Blaugrana hired a detective agency to follow the Spain international.
The newspaper also insist that the Catalan club monitored the centre-back's phone calls and looked into his bank account movements.
It is believed that Pique would sometimes spend up to €4,000 in single sittings at casinos, and on one occasion, sat up 'until 5.41am' talking on the phone.
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- Mundo Deportivo