A Dutch newspaper reported Wednesday it had given police an anonymous letter it received with a map showing a location in southern Portugal where Madeleine, who disappeared more than a month ago, might be found.
Detectives said the tip-off was one of the leads they were following in the investigation but declined to elaborate.
The location shown on the map is scrubland about 15 kilometers (9 miles) from where the girl vanished while on vacation with her family.
Madeleine disappeared on May 3 from a hotel in Praia da Luz, a resort town in Portugal's Algarve region. Her parents left her and her 2-year-old twin siblings alone in their hotel room while they dined at a nearby restaurant.
Since then, the couple has launched an international campaign to find the girl, enlisting the aid of celebrities including soccer star David Beckham and J.K. Rowling, author of the Harry Potter series.