The conservative right-wing challenger to Emmanuel Macron in the looming French presidential vote grappled Friday with a wave of defections, while hoping former president Nicolas Sarkozy would finally offer his full-throated support.

Valerie Pecresse, whose poll numbers have stagnated since winning the Republicains primary in December, suffered the high-profile desertions just days ahead of her inaugural campaign rally.

Her team is hoping the event in Paris on Sunday will inject fresh momentum into Pecresse's bid, revealing a more personal side to Sarkozy's former budget minister and now president of the greater Paris region.

On Friday, Pecresse finally met with Sarkozy for over an hour to discuss a campaign on which he has remained noticeably silent, at least in public.

"It was a conversation among friends, frank and warm," a smiling Pecresse told a scrum of journalists after the meeting, adding that she was "very happy with the meeting".

"It was very useful for me to have the advice of a former president," she said, while declining to say if she would indeed have his backing.

Several former aides of the popular former president, however, have already jumped ship, saying they would not support their party's candidate.

On Wednesday, Eric Woerth, a Republicains heavyweight and Pecresse's former colleague in Sarkozy's cabinet, surprised loyalists by announcing he would throw his weight behind the incumbent president Macron.

"I don't agree with the party's message" of a France that is "nostalgic and inward-looking," he told the Le Parisien daily -- reportedly without even warning Pecresse ahead of time.

The Republicains mayor of Calais Natacha Bouchart, also close to Sarkozy, followed suit Thursday by saying Macron had been "attentive" to her coastal city's struggle to cope with migrants trying to reach Britain by sea.

Valerie Pecresse, whose poll numbers have stagnated since winning the Republicains primary in December, suffered the high-profile desertions just days ahead of her inaugural campaign rally.
Valerie Pecresse, whose poll numbers have stagnated since winning the Republicains primary in December, suffered the high-profile desertions just days ahead of her inaugural campaign rally. AFP / JULIEN DE ROSA

And on Friday, another former Sarkozy minister, Nora Berra, told BFM television she would not support Pecresse.

Sarkozy has remained a fixture of the French right despite a series of legal convictions since failing to win his re-election bid in 2012.

His support is considered crucial for ensuring the Republicains base rallies behind Pecresse, who accuses Macron of being too weak on crime and immigration and simply "tells everyone what they want to hear".

But French daily Le Figaro reported Thursday that in private, Sarkozy has criticised Pecresse's campaign choices -- not least her choice of Paris for her first major rally -- and said "Valerie is all over the place" and "non-existent".

He is not expected to attend her rally at the Zenith concert hall on Sunday.

Macron remains comfortably ahead at 23 to 25 percent in opinion polls, and is widely expected to finish on top in the first round of voting on April 10.

Another headache for Pecresse is that the upstart far-right candidate, the former TV pundit Eric Zemmour, is holding up in the polls and remains in contention to make it to the second round of voting.

Zemmour's views on French history and immigration, expressed with the clarity of someone who spent years as a commentator on prime time television, often chime with the hard right in Pecresse's own party.

An Ipsos-Sopra Steria poll of 12,500 people published Friday put Pecresse at 15.5 percent, just ahead of far-right contender Marine Le Pen at 15 percent, while Macron stood at 24 percent.

Zemmour, whose campaign late last year appeared on the brink after a series of mishaps, climbed up 1.5 points in the polls to 14.5 percent.

Analysts say the presidential vote will almost certainly boil down to a contest on the right, with no leftwing candidate currently polling in double-digits.