The McCanns nearly handed over £25,000 to Karen Matthews to help her find her daughter Shannon, said the family's spokesperson.
Matthews, who served four years in prison after fabricating claims that her nine-year-old daughter Shannon had gone missing, would have received thousands from the family after Shannon could not be found, around year after the disappearance of their own daughter Madeleine.
The mother of Shannon and Michael Donovan, the friend of Matthews who kidnapped and drugged Shannon for 24 days in Dewsbury, West Yorkshire, decided to contact McCanns to see how their appeal to find their daughter raised £1m ($1.23m).
Struck by the mother's plight, the couple nearly handed over the cheque when police advised them to not hand over the money.
"Police advised us not to hand over money," said the McCann's spokesperson, Clarence Mitchell.
"We heard things had come to light in investigations. It is beyond belief anyone could've sought to exploit poor Madeleine's plight."
Karen Matthews' former partner Craig Meehan was attacked after a TV show which told the tale of Shannon, The Moorside, hit the screens in February.
Meehan, who was convicted of possessing child pornography, was beaten up by an angry parent after they discovered he was living just a hundred yards away from their child's school.
"One of the dads who has kids at the school grabbed him in the street and belted him and told him to get gone. And that's what he did," a parent from the school told The Mirror. "He was an idiot for thinking he could live around here and not be recognised."
The McCanns say that they receive around 150 messages on social media a day from abusive trolls about their missing daughter.
Brenda Leyland, who wrote 424 posts about the McCanns on the microblogging site Twitter, committed suicide after she was doorstepped by a journalist who wanted to know more about her online behaviour.
The McCanns'daughter Madeleine went missing in 2007 at the age of three, in Praia da Luz in Portugal.
Detectives have interviewed 60 people of interest and have looked into 8,685 sightings of Madeleine in the past decade.