Court officials contacted by Reuters said they could not immediately confirm the reports.
Alves, who has denied any wrongdoing, was taken to the Brians 1 jail outside Barcelona, said a source with knowledge of the matter.
Earlier on Friday, Alves appeared before a Barcelona judge after local police detained and questioned him. The public prosecutor had requested he be jailed without bail pending trial.
Alves' representatives did not respond to a request for comment.
Mexico's top-flight soccer division, Liga MX, said it was following the case and Alves' legal situation alongside club Pumas UNAM, where he currently plays, to determine "what is appropriate regarding his participation in the League".
Later in the day, Pumas UNAM announced they had terminated his contract with immediate effect.
"The club reiterates its commitment to not tolerate acts by any member, whoever they may be, that go against the club's spirit and its values," Pumas sporting president Leopoldo Silva said.
"We cannot allow the conduct of one person to damage our work philosophy, which has been an example throughout history."
The alleged victim had filed a complaint earlier this month and the case remains open over a crime of sexual assault, Catalonia's court system said in a statement.
Alves told Antena 3 TV earlier this month that he was at the club with other people but denied any such behaviour.
"I was dancing and having a good time without invading anyone's space," he said. "I don't know who this lady is... How could I do that to a woman? No."
Alves played for Barcelona from 2008-2016 and briefly returned to the LaLiga team for the 2021-22 season.
He has played for the Brazil national team since 2006, making 126 appearances and scoring eight goals.
