Marine Le Pen said her party would struggle to make payroll following a financial scandal.
The French far-right leader could perform poorly in parliamentary elections.
Populist politics are likely to remain in the mainstream despite Le Pen’s defeat, the third blow in six months to Europe’s far right.
In France's most tumultuous election in years, political uncertainty looks set to continue, whoever wins.
There is a burgeoning divide between the working middle class and the gilded Parisian super-rich.
The data leak emerged as polls predicted Macron, a former investment banker and economy minister, was on course for a comfortable victory over far-right leader Marine Le Pen in Sunday's election.
Marine Le Pen has a mountain to climb going into the final hours of her presidential race against Emmanuel Macron.
The independent candidate is predicted to win 62 percent of the votes on Sunday.
Macron said Le Pen was a "high priestess of fear" who would start a civil war, while Le Pen said her rival was a "darling of the elite."
The party deputy said a controversial speech was a deliberate "nod" to one given by rival François Fillon.
Polls predict Macron, a former economy minister, will win the May 7 run-off with about 59-60 percent. But the momentum has recently been with Le Pen, who has clawed back about five percentage points over the past week.
Earlier this year, Le Pen repeatedly said that, if elected, she would seek a radical loosening of the EU's structure and, within six months, call a referendum on the outcome recommending a 'Frexit' divorce.
Since taking over the leadership in 2011, Le Pen has sought to soften her party's far-right image, but for many voters the association remains.
Marine Le Pen faces a huge uphill battle to defeat Emmanuel Macron in the second round of the French election.
After Francois Fillon’s demise and Emmanuel Macron’s rise, the Russian establishment looks to Marine Le Pen.
Expatriates in seven African countries overwhelmingly backed centrist newcomer Macron, while the far-right Le Pen fared badly.
Le Pen is way down in the polls. But her base is energized, and as the French economy sputtersr and fears of Islamist militants grow, it may be too soon to discount her chances.
French newspaper Libération described the speech as "one of the most hardline of [Le Pen’s] campaign so far.”