Unhappy at losing untouchable status, Ronaldinho could quit the club with just 15 days' notice under employment rules agreed by FIFA and the European Union.
His brother and agent Roberto de Assis Moreira told Italy's Gazzetta dello Sport: "Ronaldinho wishes to stay in Spain, but if the board of Barcelona feel that he is no longer indispensable, then he will be able to leave for nothing."
The two-time FIFA World Player of the Year is under contract at the Nou Camp until 2010 and his buy-out clause - obligatory under Spanish league rules - is a staggering £85million.
But FIFA rules would allow him to leave for considerably less once he has completed three years of his current contract, signed in 2005.
Ronaldinho would be free to walk away next summer as long as he left Spain and paid compensation to his club, which makes a January move unlikely.
The settlement would be subject to legal wrangling but is likely to be around £13m.
Barcelona president Joan Laporta tried to quell the unrest, saying: "Because of injuries and travel with his national team Ronaldinho hasn't been at full strength in training and hasn't found his rhythm.
"But I don't believe he's a substitute. He's a fundamental footballer and Rijkaard knows it."