Kidnappers of the sister of AC Milan striker Ricardo Oliveira had not contacted relatives by Friday.
Maria de Lourdes Silva de Oliveira, 35, was kidnapped Wednesday morning after two hooded gunmen broke into her home in Sao Paulo. They overpowered her husband and children before taking her.
The abductors had not made any demands by Friday afternoon, and police were investigating the possible involvement of one of her sons _ a 14-year-old with a police record.
The teenager, who was not identified by police, was interrogated on Thursday and denied any involvement in the crime, authorities told local media.
Oliveira remained in Italy and had not made plans to return to Brazil.
Oliveira was regularly selected for Brazil's national team until suffering a serious knee injury and undergoing surgery last November. The striker recovered and played for Spain's Real Betis and Brazil's Sao Paulo before joining Milan this year.
The kidnapping was the eighth involving relatives of soccer players in Brazil in only two years.
It began with the mother of Real Madrid striker Robinho, who was abducted and released unharmed in 2004. This year, the sister of Palmeiras defender Michael and the mother of Santos defender Kleber were kidnapped and released unharmed.
Sevilla striker Luis Fabiano, former Sporting Lisbon defender Rogerio, Le Mans striker Grafite, and Corinthians defender Marinho also had their mothers kidnapped and released.