The man, who is accused of murder, is one of seven people the team hired by Madeleine's parents to hunt for the little girl hope to interview, a source confirmed.
Madeleine, from Rothley, Leics, was nearly four when she went missing while on holiday with her family in Portugal two years ago.
Clarence Mitchell, spokesman for the McCanns, refused to comment on the revelations, saying: "A number of individuals remain as persons of interest to the Madeleine investigators.
"However, the investigators will not be naming or identifying any of those persons of interest.
"No competent investigation would be expected to do so whilst the inquiries continue."
Madeleine disappeared from Praia da Luz in the Algarve on May 3, 2007 while her parents Gerry and Kate McCann dined with friends nearby.
Despite a massive police investigation and huge publicity worldwide, she has not been found.
in Press Association
Just in time for the Sunday British Newspapers