Arturo Vidal has accused Barcelona of being "unfair" amid claims he is owed up to €2.4 million (£2m/$2.7m) in unpaid bonuses.
According to Spanish newspaper ABC, Vidal has filed a complaint against his club to La Liga and the Spanish Footballers' Association.
It is alleged that the Chile international has only been paid €1.7m of the €4.1m he is owed.
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Vidal, strongly linked with a January return to Serie A, is frustrated at being underpaid but is leaving the legal matter to his representatives.