François Fillon, the establishment Republican candidate in France’s presidential election, is coming under increasing pressure to drop out of the race after a scandal saw him slip from first to third place in the polls.

So far he has vowed to fight on, telling his supporters: “Hold the line. We’ll get through this ordeal together and march on to victory,” in a video message posted to Facebook.

But while he still commands the support of some party members, others have called on him to stand aside to allow another candidate a chance to build a campaign ahead of the first round of voting which is just eleven weeks away.

However, there is little consensus on how a replacement might be chosen in practice, as there is unlikely to be enough time to re-run the party’s primary elections.

Alain Juppé, an ex-prime minister, and former President Nicolas Sarkozy are both in the frame to replace Fillon if he is pushed out, having come second and third respectively in the primary in November. Also named as possible replacements were François Baroin, a former finance minister, and Xavier Bertrand, a former labour minister, Euractiv has reported.

Party officials may thrash out a plan to proceed on Tuesday after the party’s deputies have reported back on how Fillon is perceived in their constituencies.

But Fillon is taking a proactive approach, calling a press conference on Monday afternoon to launch his comeback.

A source close to him told Reuters that his strategy can be summarised as “counter attack”. Fillon “plans to tell the truth to the French people” at the conference at his campaign headquarters, the source added.

Fillon slipped dramatically in the polls from odds-on favourite to third place behind the National Front’s Marine Le Pen and independent Emmanuel Macron after a newspaper printed allegations that his wife and two of his five children received nearly €1 million over several years in wages for fake jobs as parliamentary aides.

Fillon, a Catholic who has built his campaign on honest politics, has denied the claims, insisting that he is the victim of a “very professional slander campaign”.

On Saturday, activists for his campaign delivered three million leaflets entitled “Stop the Manhunt”, which asserted that the scandal was a left wing conspiracy and declared “enough is enough”.

If elected, Fillon has vowed to slash regulation to free up businesses, while also slashing the size of the state. He promised €100 billion in government spending cuts over five years, with the loss of 500,000 public sector jobs, as well as tax breaks for companies to the tune of €50 billion.

His relaunch comes as both Macron and Le Pen took to Lyon, France’s second largest city, to launch their bids for the presidency.

Taking to the city centre on Saturday afternoon, Macron, a former investment banker, presented himself as a centrist politician, saying: “I am not going to say that the left or right is meaningless, that they are the same thing. But are these divisions not a hurdle? […] I want to reconcile the two Frances that have been growing apart for too long.”

However, he then turned his focus toward his main rival, Le Pen, calling her policies a betrayal of French values of liberty, fraternity, and equality.

Le Pen, meanwhile, has released a list of 144 “commitments” to the nation, including pulling France out of the Eurozone and cutting red tape for small businesses. Addressing the party faithful at their conference on Sunday, she told supporters that she alone would protect them against Islamic fundamentalism and globalisation if elected president.