As Fillon's two closest rivals, the far-right's Marine Le Pen and independent Emmanuel Macron, began vigorously campaigning, the former prime minister appeared to believe he could ride out the storm engulfing his faltering campaign.
Fillon said he would fight to the end to defend his position as the party's nominee. A source in his camp said he would likely reinforce that message on Monday.
Defying opinion polls that show a dizzy downward slide to a point where the one-time favorite is now trailing in third place, he told supporters: "Hold the line."
"We'll get through this ordeal together and march on to victory," he said in a video message on Facebook.
Fillon's camp on Saturday distributed 3 million leaflets entitled "Stop the Manhunt", painting the scandal as a left-wing conspiracy and declaring: "Enough is enough".
The 62-year-old, a champion of free-market policies to reinvigorate France's heavily regulated economy, has seen his campaign unravel in the two weeks since newspaper Le Canard Enchaine reported his wife Penelope had been paid hundreds of thousands of euros as a parliamentary assistant for work she had not really done.
Seen two weeks ago as the comfortable favorite to win the keys to the Elysee palace, opinion polls now show Fillon failing to reach the May 7 runoff vote.