The prime suspect in the Madeleine McCann case is being investigated over a sex attack on a 10-year-old girl a month before the British toddler disappeared.

Christian Brueckner, now 43, is alleged to have exposed himself to the German child on a beach while she was on holiday with her family on the Algarve in Portugal in early April 2007.

The incident is said to have taken place in Salema, about six miles away from the scene of Madeleine’s disappearance in Praia de Luz.

German prosecutor Hans Christian Wolters confirmed the link to Brueckner in an interview with Portuguese TV station RTP on Friday.

He said details of the case were handed over by authorities in Portugal after German police requested information about any sexual crimes at around the time Madeleine disappeared.

German magazine Spiegel reported that the victim, now 23, was interviewed more than a year ago but the case was closed due to lack of evidence.

However she later told police that she recognised Brueckner from TV reports about the Madeleine McCann suspect in June, it is claimed.

Mr Wolters told Sky News that Brueckner’s lawyer had been sent the case files but added that "there is no direct connection to the Madeleine case except that the suspect is Christian B".

“In this case of 2007 he is suspected of showing himself in a sexual, offensive way in front of a 10-year-old German child on a beach,” he said.

“I cannot say exactly if he was masturbating in front of the child or if he has just shown himself naked. In Germany that is a sexual abuse of a child — and that's why we are investigating.”

Brueckner is currently in prison in Kiel, Germany, where he is serving sentences for drug trafficking and the 2005 rape of a 72-year-old American woman in Portugal. 

His lawyer Friedrich Fulscher said he denies any involvement in the disappearance of Madeleine McCann.