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.
Vidal, strongly linked with a January return to Serie A, is frustrated at being underpaid but is leaving the legal matter to his representatives.
"I'm not in charge of that - that's why I have my agent, my lawyer, who takes care of the awards and stuff," Vidal told Chilean radio station ADN.
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"It seems unfair to me if money is missing, but it is an issue that is alien to what we are experiencing today."
Vidal has started just four La Liga games for Barcelona this term, in sharp contrast to his first season at Camp Nou when he made 53 appearances in all competitions to help the club win the Spanish Super Cup and La Liga title.
His lack of regular action this campaign has sparked speculation about a move away from the club next month.
Speaking about his future earlier this week, Vidal refused to rule out a move to Inter in the upcoming transfer window.
However, the ex-Juventus and Bayern Munich star - a reported €18m (£15.3m) signing in August 2018 - is not thinking about his future while back in his native Chile for a short Christmas break.
"It's a subject I said when I arrived here that I'll talk about it when I'm there [in Spain]," he said.
"I'm on holiday and I just want to talk about what's going on here.”
Vidal began his career with Colo-Colo back in his native Chile before moving to German side Bayer Leverkusen in 2007.
After four seasons in Germany he moved to Juventus in 2011, where he won seven major trophies including four Serie A titles.
The 32-year-old then joined Bayern in 2015, winning three successive Bundesliga titles, before his move to Barcelona.
Vidal has also earned 115 caps for Chile and was part of the squad that won the 2015 Copa America.