The voting of who will become the conservative candidate for the French presidency and likely favorite to win the presidential election itself next year are due to be held on Sunday, Reuters reported on Friday.
Sunday's vote will put two people forward to a run-off second round a week later. And it seems that centrist ex-prime minister Alain Juppe is holding onto a shrinking lead.
Opinion polls show him winning both primary rounds and then going on to win a probable face-off against far-right National Front leader Marine Le Pen next May and become head of state.
The other frontrunners are ex-president Nicolas Sarkozy and Francois Fillon, who was Sarkozy's prime minister between 2007 and 2012.
Sarkozy has long been Juppe's main rival, but Fillon has come from behind in the opinion polls in recent days, making the race even harder to call. Fillon was seen as the winner in Thursday's final debate before the weekend vote.
In addition, anyone can vote in the primary, which opens the way for tactical action by left-leaning and far-right voters.
Meanwhile, lack of confidence in pollsters, who failed to predict Donald Trump's U.S. election win and Britain's vote to quit the European Union, has added to the uncertainty about the outcome of both the primaries and the election itself.Particular focus is on Le Pen
because she represents the same populist, anti-globalisation, anti-immigration positions that handed unexpected victories to Trump and Britain's Brexit camp.
So market analysts are taking the possibility Le Pen could become president more seriously, an event which some believe could spell the end of a weakened European Union and of the euro zone.
Polls have consistently shown Le Pen is very unlikely to win the presidency. The country's electoral system requires her to win over 50 percent of votes in a second-round run-off, and she has persistently polled only around 30.
Juppe was confident on Friday that no such upset will happen."I am not Hillary Clinton,"
he said on public radio in a reference to the losing candidate in the U.S. presidential race. "And France is not America."
France's ruling Socialists are deeply divided
and seen as unlikely to figure beyond the first round of the election itself - leaving the way clear for whoever emerges as victor in the conservative primaries to face Le Pen in the deciding round.