The German suspect, Christian Brueckner, lived in the Algarve at the time when McCann vanished, and is due to be released from prison in Germany. He was first named as a suspect by British and German police in 2020.
"We are aware of the pending release from prison of a 49-year-old German man who has been the primary suspect in the German federal investigation into Madeleine's disappearance," Detective Chief Inspector Mark Cranwell of Britain's Metropolitan Police said in a statement on Monday.
"We can confirm that this individual remains a suspect in the Metropolitan Police's own investigation."
McCann went missing on May 3, 2007 while on holiday with her family in the Algarve town of Praia da Luz, sparking a frenzied search and gaining the attention of the world's media. She has never been found.
The German suspect had refused a request for an interview from British police, the police statement said, adding that officers will continue to pursue any viable lines of inquiry.
"We can provide no further information while the investigation is ongoing. Any questions about the conditions around his release should be directed to the German authorities," the statement added.
German police said in June 2020 that McCann was assumed dead and that Brueckner was likely responsible. Brueckner has denied any involvement and has not been charged with any crime related to the case.
The convicted child abuser and drug dealer is behind bars for raping a 72-year-old woman in the same area of the Algarve.
Ahead of his expected release, Portuguese and German police spent four days in June searching for evidence related to McCann's disappearance in the Algarve.
