Zuniga has signed to 2018, with the deal crying a mooted €35 million buyout clause.
"The clause is proportional to the value of the player" Riccardo Calleri told Radio Marte. "It's a major deal for Zuniga and for the club.
"We signed a long contract, so he might well end his career at Napoli - we will see in five years.
"The clause is useful and proportional to Zuniga's value. All I'll say is that it's more than 30m."
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