The incident happened after Christian Brueckner, who is serving a prison sentence for a drug conviction, was taken to Braunschweig state court on Monday for a routine hearing in that case.
Court spokeswoman Jessica Knab-Henrichs told The Associated Press that he was briefly treated in a hospital for two broken ribs, and was then returned to the court where the hearing took place.
The incident is under investigation and further details on what happened at the court were expected to be released later, she said.
Although Brueckner is a suspect in the McCann case, prosecutors have said they do not have enough evidence to hold him on the McCann case alone.
In addition to the drug trafficking sentence, which Brueckner will have finished serving in January, he was convicted in 2019 of the 2005 rape of a 72-year-old American woman in Portugal and sentenced to another seven years.
That conviction is under appeal.
Madeleine McCann was three at the time of her 2007 disappearance from an apartment while her family holidayed in the seaside town of Praia da Luz in Portugal’s Algarve region.
German authorities in June said they had identified the 43-year-old German citizen as a suspect in the case and were investigating him on suspicion of murder.