Gabriel joined Inter Milan last week for a reported 29.5 million euros ($32.9 million) after the Italian club beat off interest from Juventus, Manchester United and Chelsea, reports Xinhua.
But Barcelona claim the move breached their right for first refusal to sign the 19-year-old, Globoesporte reported on Saturday.
The Catalan outfit has alleged it was notified of the Inter proposal a day before Gabriel signed with the club.
The 2013 agreement -- part of the deal that saw Neymar move to the Spanish city -- stipulated that Barcelona be given at least three days to match an offer for Gabriel from another club, Globoesporte said.
Gabriel is considered one of the brightest talents in Brazilian football. He has scored twice in four senior international appearances for Brazil and was part of the Selecao team that won the gold medal at the Rio Olympics last month.
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