The court postponed the trial by a week to rule on whether the lay judge should be removed over Tweets in which she allegedly called for the killing of former Brazilian President Jair Bolsonaro and of an animal torturer.
"Such a lay judge has no business participating in a fair criminal trial," defence lawyer Friedrich Fuelscher told reporters outside the court in Brunswick, northern Germany.
German media also reported that lawyers also cited the lay judge's work as a child psychologist as a potential source of bias in a case involving the sexual abuse of several children.
Christian Brueckner, who is already behind bars in Germany for raping a woman in the part of Portugal's Algarve region where McCann went missing, faces three charges of aggravated rape and two of sexual abuse of children committed between 2000 and 2017.
Brueckner has denied being involved in McCann's disappearance in 2007 and has not been charged with any crime related to it.
Among the charges he was due to answer on Friday were the rape of a woman in her 70s in her home in the Algarve, the sexual abuse of a girl aged at least 14, and the 2004 rape, at knifepoint in her home, of a young woman - an act he is accused of recording on video.
Portuguese prosecutors investigating the disappearance of McCann identified as an official suspect a person whose details corresponded to those of Brueckner two years ago.
German police said in June 2020 that McCann was presumed dead and that Brueckner was likely responsible for it.
McCann disappeared from her bedroom on May 3, 2007, during a family holiday while her parents were dining with friends nearby in the resort of Praia da Luz.
(Reporting by Thomas Escritt;Editing by Alison Williams and Nick Macfie)
By Oliver Denzer
