As more embarrassing revelations for Fillon emerged on Thursday and the police widen their investigation into the fake job claims surrounding his wife and children, it looks like the nails are being prepared for the coffin of François Fillon's political career.
Falls in opinion polls and growing panic and dissent among his Republicains party may force the self-proclaimed sleaze-free Fillon out of the race for the Elysée long before the police decide whether he and his wife have a case to answer.
Which leads on to the question: what happens to the French election race if or when Fillon is felled?
In short, no one quite knows, but behind the scenes there has been increasing talk of Les Republicains MPs desperately trying to come up with a Plan B.
If Fillon decides to step down or is forced to by his party (as now seems the likeliest option) or even by police bringing charges against him (unlikely given the investigation could take months) then his party have few options.
Holding another primary election is not considered a realistic option as it would take too long to organise, given that the official deadline for candidates to declare their bids is March 17th. The last thing the party wants is another divisive battle between rivals.
There is talk of party chiefs nominating a new candidate or party members holding a one-off vote.
Neither option is of course ideal given the delight felt among Les Republicains after Fillon won 66 percent of 4.3 million votes in November's primary, which was seen as a mandate to go on and win the presidential election in spring.
And what about his beaten rival Alain Juppé, surely he is the obvious guy to replace Fillon?
He would be for most centre-right supporters, but Juppé has repeatedly ruled himself out in recent days.
On Wednesday night as Fillon lambasted a Socialist government-organised “institutional coup d’etat” against him, Juppé again declared that he would not be part of any Plan B.
An MP from his Republicans party said Thursday that an open letter was being drawn up by some members of the party calling for Fillon to be replaced by his 71-year-old rival Alain Juppe if he decides to stand aside.
At the moment, while Fillon is angrily contesting the allegations, the likes of Juppé and other party bigwigs have not wanted to be seen as breaking ranks. But things are changing rapidly.
“It may take a few days,” Bruno Jeanbart from polling agency Opinion Way tells The Local. “No one wants to be first to say 'I'm available, because they will be finished, but everyone is waiting.”
So, if Juppé refuses, who else is there?
A man named Nicholas Sarkozy could also be a wildcard option. Sarkozy, a former president of course, was knocked out in the first round of the primary and would probably secretly relish another shot at the top job if it fell into his lap.
According to reports on Thursday Sarkozy was “savouring” every moment of Fillon’s struggles. However his entourage told Le Parisien newspaper a Sarko comeback was “unthinkable”.
Since Wednesday there have also been reports of former ministers François Baroin and Laurent Wauquiez being touted as replacements for Fillon as well as Xavier Bertrand, the president of the region Hauts-de-France.
Interestingly, on Wednesday L’Express newspaper reported that the domain names Baroin2017.fr, Wauquiez2017.fr and Bertrand2017.fr had been bought up since the Fillon allegations first emerged.
The website purchases may have just been opportunistic but it could also be a sign perhaps that someone in the party is preparing for the worst.
There has also been a suggestion Nathalie Kosciusko-Morizet, another defeated candidate in the primary, could be a choice.
But would any of these candidates really have a chance of winning? It would be an uphill battle for all of them.
Fillon was a one-time shoo-in for the Elysée: who benefits if he quits the race?
Given the unpopularity of the current Socialist government and the slim chances of a resurgent Marine Le Pen gaining power due to France’s two-round electoral system in which voters have traditionally acted tactically to keep out the National Front, the 2017 election was considered Fillon’s to lose.
But if he stays in the race it appears that’s exactly what will happen. Latest polls put him behind both the wildcard centrist Emmanuel Macron (see photo above) and Le Pen in the first round.
Polls suggest Macron has benefited the most from Fillon’s torment and ironically the 39-year-old maverick former economy minister may be hoping he somehow stays in the race as a critically wounded runner.
If someone like Juppé replaces Fillon, then the mayor of Bordeaux, who is more of a centrist and less socially conservative, could seriously damage Macron’s hopes of making it to the crucial second round.
Fillon, with his Christian heritage and plans for radical austerity and severe labour reforms, was seen as an ideal candidate for the progressive Macron as well as for Socialist candidate Benoit Hamon, whose radical ideas to tax robots and introduce universal basic income offered a clear alternative to voters.
Le Pen on the other hand might be thrilled to see the back of Fillon.
Fillon’s victory in the primary was not welcomed by Le Pen’s team. His tough stance on issues of security, identity and fundamental Islam as well as his opposition to gay marriage and abortion would appeal to many of Le Pen’s traditional electorate.
But if he goes and is replaced by someone like Juppé, who promised a “happy identity”, then those voters would presumably be left with only Le Pen as their chosen option in 2017. In any case she is widely expected to make the second round runoff vote. Fillon's fall could just help her take the next step, always seen as impossible until the US voted for Donald Trump in November.
One of the most unpredictable French election races in years could be about to blown wide open and no one really knows what will happen.
“This election race has already been incredible,” says Opinion Way's Jeanbart. “Nothing will surprise us anymore.”