The French Muslim woman, who wants to remain anonymous and uses the pseudonym “Marie”, claims to have suffered multiple rapes in France, Brussels and London between 2013 and 2014.
She has accused Ramadan, 55, of subjecting her to violent and sexually degrading acts during a dozen meetings, often in hotels at the sidelines of conferences.
“Marie tried in vain to escape the influence of Mr Ramadan who did not stop threatening her,” according to a judicial source, discussing the period
between February 2013 and June 2014.
Ramadan, a prominent TV pundit and Oxford University professor whose grandfather founded Egypt's Muslim Brotherhood movement, was detained on
February 2 over charges he raped two Muslim women in France, which he denies.
French authorities ordered Ramadan to be placed in custody after he was charged, judging him a flight risk.
His lawyers unsuccessfully proposed handing over his Swiss passport, bail of 50,000 euros ($62,000) and daily check-ins at a police station to secure his release.
A professor of contemporary Islamic studies at Oxford, Ramadan has been on leave since November after the allegations emerged.
One of European Islam's best known figures, he has dismissed the accusations against him as a smear campaign by his enemies and his lawyers
argue there are inconsistencies in the women's accounts.
His supporters — including two million Facebook followers — have lashed out angrily at his arrest, with many complaining that he has been unfairly targeted because he is Muslim.