The presidential candidate has dismissed the allegations and vowed to provide evidence to support
He has now vowed to produce evidence to counter explosive the claims regarding $540,000 (£458,000), it emerged today.
The rightwing Mr Fillon, who polls show is likely to reach the second round of May's election, is facing an investigation into claims he handed his British-born wife Penelope a fictitious paid role as a parliamentary aide.
Fillon's campaign manager, senator Bruno Retailleau, said the candidate's lawyer would contact the national financial prosecutor's office and "take them a certain number of documents".
Mr Retailleau said: "We will give all the pieces (of evidence) to the investigators very quickly.
"It will then be between the investigators and Francois Fillon."
He adding: "I tell you, this thing is going to fizzle out very quickly."
Mr Fillon is accused of paying his wife for the fictitious role of parliamentary aide
The allegations are potentially damaging to the 62-year-old, who owed some of his surprise victory over Nicolas Sarkozy in the rightwing primary contest to a "clean" image, contrasting with the former president's legal woes.
I tell you, this thing is going to fizzle out very quickly
Bruno Retailleau, Campaign manager
The claims first surfaced in the Canard Enchaine weekly, which mixes satire and investigative reporting.
The paper said it had been unable to find anyone who remembered Penelope working in parliament.
Mr Fillon has dismissed the allegations, which are dominating coverage of the campaign, as "mudslinging" and "misogynistic".
The right-wing candidate looks set to reach the second round of the France's presidential race
In a statement later Wednesday, Mr Fillon said he hoped to speak to investigators "as soon as possible (to) set out the truth", adding that the claims were "baseless".
Fillon's spokesman Thierry Solere confirmed to AFP on Tuesday that Penelope had worked for her husband and said the arrangement was "common" among French MPs.
The candidate will also appear on France's main evening news show on TF1, his camp said.
British-born Penelope Fillon has previously tried to seperate herself from her husband's career
Hiring family members is not against the rules if the person is genuinely employed, but attention is focused on precisely what work Penelope carried out for a salary of sometimes around 7,000 euros a month.
The Canard Enchaine alleged that Penelope received the money between 1998 and 2012.
It said she also worked for a periodical, Revue des Deux Mondes, owned by a friend of Francois Fillon, between May 2012 and December 2013.
Francois Hollande Fast Facts
Thu, December 1, 2016
Here is a look at the life of Francois Hollande, President of France since 2012.
1 of 9
December 1st, 2016: Francois Hollande decides not to run again in the next France presidency.
The silver-haired mother-of-five has kept a low profile in Mr Fillon's nearly four-decade political career, telling a newspaper during the rightwing primary campaign last year: "Until now, I have never got involved in my husband's political life."
The couple, who met in their early twenties, live in a chateau near Le Mans in northern France.