A Malawian child rights group has said it wants to stop Madonna adopting a child from the African country.
Madonna visited several orphanages while in Malawi
The organisation, Eye of the Child, said it would seek a court injunction if the government did not halt its interim order approving the adoption.
"It's not like selling property," the group said in a statement.
Madonna is thought to have flown out of Malawi on Friday without the child, having filed adoption papers to adopt the one-year-old, called David Banda.
Eye of the Child said it was "about safeguarding the future of a human being who, because of age, cannot express an opinion".
Another Malawian human rights group, the Civil Liberties Committee, said it would back the Eye of the Child in its bid to stop the interim adoption approval.
Madonna and husband Guy Ritchie left Malawi without the child, a senior immigration officer told the Reuters news agency.
Madonna recently finished her world Confessions tour
"The baby hasn't gone yet because immigration is still trying to process his passport," he said.
Malawian officials said they expected David to spend time with Madonna while waiting for final adoption approval - a process which could take up to two years.
Embassy officials will monitor how the child gets on, and a decision will be made based on their findings, according to a senior government official.
The child had been cared for at the Home of Hope Orphan Care Centre in a village close to the border with Zambia, after his mother died a month after his birth from related complications.
The boy's father, Yohame Banda, has agreed to the adoption.
And the chief of Lipunga, the village where the child was born, said he also approved.
"If we didn't send David away to the orphanage we would have buried him," he said.
But the boy's uncle, Pofera Banda, said he wanted to know how the family would benefit if the adoption went through.
"We have seen other parents at the mission who have had their children adopted still living in their poverty.
"They have not seen their children - all they see is pictures sent to them. We don't want that to happen to this family," he said.
Madonna said she had travelled to the region with her husband, film-maker Guy Ritchie, to help fight poverty and the problem of HIV and Aids.
She has pledged to donate about $3m (£1.6m) to help 900,000 orphans in Malawi.
The 48-year-old already has two children, five-year-old son Rocco and nine-year-old daughter Lourdes.