Mendeson appeals made by Goldman and Brazil's attorney general seeking to lift a stay on a lower court's order that Sean Goldman be handed over to his father.
But Mendes has already decided and will not rule on his own for the boy's return, the source, who requested anonymity citing no authority to speak on the matter.
Mendes, instead, will defer to the entire Supreme Court, which is expected to rule on the case in February.
Goldman has been battling for custody of Sean since his then-wife Bruna Bianchi took him to Brazil in 2004. She decided to stay, divorced Goldman and remarried, before dying while giving birth to a daughter last year.
Since then, Sean Goldman has been raised by his Brazilian stepfather and his maternal grandparents, who have fought to retain custody. 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 did not say whether he would accept the invitation if the case was not resolved this week.
Asked if Sean's Brazilian family would be able to visit the boy if he won his appeal, Goldman said yes. "I will not do to them what they've done to Sean and me," he said.
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. State Department pressed for the boy to be returned. But a Brazilian Supreme Court justice on Thursdayordering Sean to be turned over to his father.
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.
"We're raising the white flag and saying: 'Let's get together, let's talk. We're the adults, we have responsibilities, so let's start to have a constructive conversation,'" Tostes said.
Goldman, however, was in no mood to negotiate.
"This isn't about a shared custody - I'm his dad, I'm his only parent," Goldman said. "This isn't a custody case - it's an abduction case."
After many disappointments, Goldman said he was taking nothing for granted.
"Until my son and I are on a plane together and those wheels are up, I'll be no less determined and no less hopeful for that day to come," he said.
He said he can't wait to make up for lost time.
"I have five years of love to give him, so he's going to get an extraordinary amount," Goldman said. "With love and patience, we will heal."