Detectives believe a staff member at the complex in Praia Da Luz, Portugal, may have hid secrets that could have helped the initial investigation.
While there is no suggestion the employee, who is said to be a Portuguese man who speaks some English, was involved directly in Madeleine’s disappearance, it is thought he may have information.
The Daily Mirror reported a Portuguese police source as saying: “British officers are convinced he knows more than he was previously saying and are very keen to question him.
“They are not suggesting he stole Maddie but he may know people who could have been involved after a burglary went wrong. The investigation in Britain seems to be grinding to a halt and they want to rule him out of the case if not rule him in.
“Then detectives know they have done everything in their power to try to solve the case.
“This Portuguese man used to work at the club resort, he speaks a bit of English.”
Another source reportedly said: “There is just one person detectives want to speak to who was near to the area Madeleine disappeared from 10 years ago.
“An international search has been under way to find them.”
Scotland Yard investigators this week received an additional £85,000 from the government to continue their work for another six months.
A re-investigation into case was launched in 2011 after the initial one by the Portuguese authorities was deemed insufficient.
Madeleine was nearly four when she vanished in May 2007 from her family’s holiday apartment in Praia da Luz as her parents dined with friends at a tapas bar nearby.
The McCanns have spoken of their bitter regret about leaving her and two-year-old twins Sean and Amelie alone.
The missing girl would now be a teenager. The family has never given up the search for their daughter and remain hopeful she is alive.