Oscar Pereiro tested positive for a banned substance during his second-place finish at the 2006 Tour de France, French newspaper Le Monde will report on Friday.
The Spaniard could be named Tour champion if race victor Floyd Landis is convicted for his positive testosterone test later this year by American authorities.
According to the Le Monde report, however, the Caisse D'Epargne leader Pereiro tested positive for the banned asthma treatment salbutamol twice during the 2006 Tour, on the July 17th stage 14 between Montélimar and Gap and the July 19th stage 16 between Bourg-d'Oisans-La Toussuire.
The French Anti-doping Agency (AFLD) president Pierre Bordry told L'Equipe on Thursday: "This rider tested positive twice. Once in Gap and another time in La Toussuire.
"Each time, he wrote on the test report that he had a TUE (Therapeutic Use Exemption). But I am asking him to provide us with the medical elements that justify him taking salbutamol."
Mathieu Desplat, a spokesman for Tour organisers the Amaury Sport Organisation, told Reuters on Thursday: "We are waiting until Jan. 25 when Pereiro's case will be reviewed by AFLD before taking any action."
The AFLD has reportedly sent three letters requesting Pereiro's medical explanation from the rider and as of Thursday was yet to receive any response.
The AFLD has also requested the UCI offer their justification for clearing Pereiro, but have not yet heard an adequate response.
"We will not be satisfied with an administrative file," said AFLD president Pierre Bordry on what he was expecting to receive from the UCI.
The AFLD was set to review the case on Thursday, and Le Monde said the agency would open disciplinary proceedings against Pereiro if it is not convinced of the Spaniard's argument.
If the AFLD charged and then convicted Pereiro, he would be banned from riding in the country and stripped of his second-place, which means he would be denied a starting spot at this year's Grande Boucle.