The escalation is another blow to the conservative candidate whose status as favorite to win the presidency has faded since the 'Penelopegate' affair -- named after Fillon's wife -- first surfaced a month ago. But it may not stop him from standing in April-May vote. By involving a magistrate in what had so far been a preliminary probe led by police, the prosecutor is putting more resources into the investigation. The inquiry will examine possible misuse of public funds and a lack of full and proper disclosure, according to the prosecutor's statement that was issued as Fillon took to the stage at a campaign rally near Paris. The judge can decide to drop the case, place the 62-year-old former prime minister under formal investigation, or send the case to trial. It was not clear, however, if the inquiry could be concluded before the two-round election, scheduled for April 23 and May 7, but the French judicial process would not typically wrap up such a case in the nine weeks between now and the poll. Under French law, if Fillon were to win the presidential race the investigation would be suspended during his time in office. Fillon has denied any wrongdoing and says his wife was paid hundreds of thousands of euros for genuine work as his parliamentary assistant, though he has acknowledged giving her the work was an error of judgment. INVESTORS CONCERNED BY ELECTION Fillon made no reference to the prosecutor's decision at his rally, at which his supporters cried out 'Fillon, President!'. Fillon has pledged to stay in the race come what may, after saying for weeks that he would step down if he were put under formal investigation. 'You are my companions, and with you at my side I can feel your energy that will give me the strength to win,' Fillon told the rally. Nevertheless, the issue has unnerved investors who fear Fillon's campaign woes have handed the anti-euro, anti-immigration Marine Le Pen of the National Front a higher chance of winning the presidency. Opinion polls show Le Pen leading a fragmented field in the first round but then losing to independent centrist Emmanuel Macron in a second round run-off. Macron has been favorite to win the presidency since the Fillon scandal broke on January 25. Fillon - who has long cultivated an image of probity and criticized people for taking government handouts - has been heckled for weeks by protesters at campaign outings. Macron got a boost on Friday when German Chancellor Angela Merkel said she was ready to meet him. Le Pen, however, was roundly criticized by the French mainstream political establishment after she refused to attend a summons for questioning by police over allegations that she made illegal EU payments to her staff.