Portuguese police are investigating whether a suspect in the Madeleine McCann case may also be linked to a rape in the Algarve three years prior.
Child sex offender Christian B is being investigated over possible links to an attack on an Irish woman.
Hazel Behan, 37, waived her right to anonymity to speak about the assault near Praia da Luz in 2004.
Officers say they will pass on any evidence to their German counterparts probing the disappearance of Madeleine.
A police source told BBC Europe correspondent Gavin Lee they have “credible information” that 43-year-old German man Christian B may be linked to the rape of Ms Behan, who was working in the region as a holiday rep in 2004.
No suspect was ever identified in her case and forensic evidence is understood to have been destroyed.
However, it has since come to light that a year after her alleged attack, Christian B was convicted of a similar rape in Praia da Luz.
Ms Behan said she felt physically sick when she learned about Christian B, following a police appeal for information.
The Guardian reported that detectives in Portugal collected the archived case file on her assault last week, quoting a source in the public prosecutor’s office.
Rape cases that took place more than 15 years ago cannot be tried in Portugal.
Christian B, who is currently in prison in Germany, was revealed as the main suspect in Madeleine’s disappearance, as German and UK police made a fresh appeal for help in the case in June.
He is believed to have been in the area where Madeleine, aged three, was last seen while on holiday in Praia da Luz with her parents and siblings.
The Metropolitan Police, who are working with their German and Portuguese counterparts, have said the case remained a “missing persons” investigation in the UK because there was no “definitive evidence” as to whether Madeleine was alive or not. But German prosecutors have said she is “assumed” to be dead.