Brazilian soccer star Ronaldinho will remain behind bars following his arrest over a fake passport allegation, an appeals court in Paraguay has ruled.

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 had filed another appeal on Thursday, two days after another court rejected their request to release the pair on bail or to house arrest.

But this appeal has now been rejected.

"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.

Ronaldinho and his brother 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.

He is being held in police cells alongside 25 police officers accused of various crimes and four politicians.