Mr. Arend has denied the allegations.

Mr. Ramadan, 55, is a well-known Islamic scholar and the grandson of Hassan al-Banna, who founded the Muslim Brotherhood in Egypt in the 1920s. The group has become one of the most influential transnational Sunni Muslim movements in the world.

Mr. Ramadan teaches contemporary Islamic studies at Oxford University and is the author of a dozen books in English on modern Islam and the Western world.

A familiar figure at conferences and in the news media, he is also a major presence on social media, with two million Facebook friends and more than 200,000 followers on Twitter.

Neither Mr. Ramadan nor his lawyer has responded to the accusations by the second woman. In a Periscope video posted on Twitter that he made several days ago after the first complaint, Mr. Ramadan said that he would not comment and that he would trust the courts to see that justice was done.

Asked about the latest allegations, his lawyer, Yassine Bouzrou, said he had not been informed, Le Monde reported.

Ms. Ayari, 40, said she had been corresponding with Mr. Ramadan on Facebook and had often asked him for advice on religion, until one day he proposed a meeting at the hotel where she said she was attacked.

The author had written about the assault in her book “I Chose to Be Free,” an account published in 2016 of how she been drawn to Salafism, a radical Islamist ideology, and then fought to break away from it. But she did not name the attacker, she said, because he had threatened her and her children.