Paris - French 3 000m steeplechase specialist Ophelie Claude-Boxberger has tested positive for EPO, a source close to the case said on Tuesday.
This is third doping case in French athletics in less than a year.
Paris' Public Prosecutor's Office confirmed it had opened a "preliminary investigation on 14 October into offences under anti-doping and poisonous substances legislation" following a report from the French anti-doping agency (AFLD).
"I learned once again from the press that there would be a positive test, there was no confirmation from the AFLD," said Andre Giraud, the president of the French Athletics Federation (FFA).
He said a change of law in March means "we have been kept out of the proceedings. We no longer have disciplinary powers. We are not happy about this type of affair. They create unease, there is no denying it."
Claude-Boxberger, 31, had a difficult time at September's World Championships in Doha as she finished a distant last in her heat and social media posts suggested she was in a relationship with the French team's medical director Jean-Michel Serra.
He quit his position midway through the championships "for personal reasons".
In June, Serra, without warning his superiors, complained about the number of doping tests Claude-Boxberger had been subject to by the French authorities. At the time, he denied any relationship with the runner.
Spe15.fr, a French website specialising in doping in middle-distance running, reported Claude-Boxberger's home had been searched.
French newspapers reported police had visited the headquarters of the FFA.
During the World Championships, German broadcaster ARD reported another French runner, Morhad Amdouni, the 2018 European 10 000m champion had exchanged WhatsApp messages with a person asking him for payment for an EPO purchase. Amdouni denied the accusations.
On Wednesday, another French athlete, marathon runner Clemence Calvin, faces a disciplinary hearing along with her husband and coach Samir Dahmani, for avoiding an unannounced test in Morocco in March.
"It's very good that there's a massacre right now, it proves that things are opening up and moving towards a cleaner sport," said decathlon world record holder Kevin Mayer as the French team assembled on Sunday for a training camp to launch their Olympic preparations.
"It drives me crazy. I don't know who's doped in the French team... The only buddy who doped in the French team was Quentin Bigot and I haven't wanted to have any personal relationships with him since," he added.
Of the athletes with Mayer, only Bigot, a hammer throw silver medallist in Doha but suspended for two years for using an anabolic steroid in 2014, offered a more nuanced answer opinion.
"Am I the best person to talk about this," he said.
"It's sad. I've been there, I know what it is like, it's especially hard for the athlete and everyone around them. We shouldn't be happy about this kind of news."