The official said Monday that the ruling by Chief Justice Gilmar Mendes was being delayed for a day past the original target date. The official agreed to discuss the matter only if not quoted by name because she was not authorized to discuss the case.
David Goldman, who has pledged to fight for his son, Sean, as long as it takes, was still holding out hope of being reunited in time to celebrate the holidays with him in the United States.
Mendes appeared close to ruling on appeals made by Goldman and Brazil's attorney general seeking to lift a stay on a lower court's order that Sean be handed over to his father.
If Mendes lifted the stay, lawyers in both camps said Sean's Brazilian relatives could still appeal to the nation's highest appeals court - but it was questionable whether that court would be willing to review the case if the Supreme Court backs a lower federal court ruling awarding custody to Goldman.
New Jersey Rep. Chris Smith, in Brazil to support Goldman, expressed optimism Monday.
"I think it is only a matter of when and not if, and we are hoping that the abductors will convey this young boy ... as soon as the chief justice renders his decision," the Republican congressman said.
Goldman, 42, launched his case in U.S. and Brazilian courts after Sean was brought by his mother in 2004 to her native Brazil, where she then divorced Goldman and remarried. She died last year in childbirth, and the boy has lived with his stepfather since.
The lawyer for the boy's Brazilian family offered to negotiate a settlement, and the family also invited Goldman to spend Christmas with them. Goldman has not said whether he would accept the invitation if the case was not resolved this week.
The case has affected diplomatic ties between Brazil and the U.S., reaching talks between President Barack Obama and his Brazilian counterpart, Luiz Inacio Lula da Silva. A U.S. senator, reacting to the case, has blocked the renewal of a $2.75 billion trade deal that would lift tariffs on some Brazilian exports.
The U.S. Department of State pressed for the boy to be returned. But a Brazilian Supreme Court justice last week stayed a lower court decision ordering Sean to be turned over to his father.
Goldman and Brazil's attorney general filed appeals asking the Supreme Court to overturn the justice's decision to block Sean's return while the court considers hearing direct testimony from the boy.
The Brazilian family's lawyer, Sergio Tostes, told the AP he would like to see a negotiated settlement, saying he wanted to end the damage being done to Sean and to U.S.-Brazil relations.
But Goldman said that as the child's only surviving parent he wasn't interested in shared custody.
AP Television News Producer Flora Charner contributed to this report.