The 39-year-old World Cup winner and his brother, Roberto de Assis Moreira, have been held in a police cell since last Friday accused of entering Paraguay using fake passports.
Lawyers representing the brothers filed an appeal on Thursday, two days after another court rejected their request to release the pair on bail or to house arrest.
“The risk of flight and the risk of obstruction of the investigation, which is the basis of the detention measure against the Assis Moreira brothers, has not changed,” the appeals court judges said in a statement.
Sixteen people have so far been implicated in the fake passport scandal, public prosecutor Federico Delfino said.
The brothers arrived in Asuncion from Brazil last week and showed their passports to immigration police, who did not immediately notice any problem.
Hours later, when the passports were determined to be fake, investigators raided the football star’s hotel room and seized the brothers’ identity cards and travel documents.
Two-time world player of the year, Ronaldinho said the passports had been given to him by people who had invited him to attend conferences sponsored by a charity working with disadvantaged children.
An arrest warrant has been issued against the Paraguayan businesswoman in charge of the charity foundation that invited Ronaldinho.
The country’s migration director has resigned over the affair.
One of the investigating prosecutors, Marcelo Pecci said the fake documents found in the possession of the Brazilian brothers had cost $18,000 to produce.
Two detained men, Sebastian Medina and Ivan Campos, are accused of the “indirect production of public documents with false content, the use of public documents with false content and criminal association.”
Ronaldinho, considered one of the greatest footballers of all time, was a star of Brazil’s 2002 World Cup win and played for European giants Barcelona, Paris Saint-Germain and AC Milan, among others.
He is being held in police cells alongside 25 police officers accused of various crimes and four politicians, including the former president of the Paraguayan Football Association and an ex-president of the House of Deputies.
Ronaldinho has taken part in a football match involving inmates and riot police, a police source told AFP.