A request for fresh cash from the Home Office is yet to be made, despite financial support for the search expected to run out by the end of the month.
More than £11million has been spent on the probe to find Maddie after she disappeared while on holidays with her family in Portugal more than a decade ago.
But despite the global search, there has been no significant clues as to what could have happened with Maddie's parents Kate and Gerry continually fighting for more funding.
A source close to the family told the Mail Online: "They have been here before. They simply have no idea if the search will abruptly come to an end or will carry on. It is a daunting prospect they face once more."
They added: "Kate and Gerry are grateful to the Metropolitan Police for everything they have done over the years and hope of course that the inquiry into their daughter's abduction will continue if more funds are requested and made available."
It comes after it was revealed detectives involved in the case have been secretly visiting Portugal in the past year.
Five return flights were booked to the country, where the toddler from Leicestershire disappeared in 2007, Met Police documents revealed.
Officers have also poured through 40,000 documents filed by Portuguese officials who have been involved in the investigation.
Maddie was three when she disappeared from a holiday apartment in the Algarve region of Portugal while her parents dined with friends nearby.
She disappeared on the evening of May 3 from her bed in a holiday apartment in Rua Dr Agostinho da Silva, Praia da Luz, where she had been sleeping with her brother and sister.
She would have turned 15 on on May 12, 2018.
A number of potential leads have emerged since the little girl vanished, but none amounted to anything and no arrests have ever been made.
In 2010, Maddie’s distraught parents met with then-home secretary Theresa May to talk about the hunt for their daughter.
The following year, Scotland Yard launched its own review, named Operation Grange, into the case at the behest of the future PM.
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