Anti-doping officials in Australia threw out the case for lack of scientific proof, but the sport's governing body wants the investigation reopened, the paper said.

Thorpe retired in November at age 24. He did not compete in another major international meet after the 2004 Olympics.

L'Equipe said Thorpe turned up irregular levels of testosterone and luteinizing hormone in a test on May 2006. Synthetic versions of testosterone, the male hormone, can act like steroids to improve performance. Luteinizing hormone is released by the pituitary gland and produces testosterone in men.

FINA, swimming's ruling organization, has appealed to the Court of Arbitration for Sport, the highest tribunal in the sports world, to overturn a decision by Australia's anti-doping agency to close the case, L'Equipe said.

CAS secretary-general Matthieu Reeb did not answer messages from The Associated Press left at his home and the court's headquarters in Lausanne, Switzerland.

An official at FINA's headquarters, also in Lausanne, said she could not comment because all the organization's senior officials were in Melbourne, Australia, for the world swimming championships.

The news broke in the middle of the night in Melbourne. FINA president Mustapha Larfaoui was scheduled to speak at a news conference there Saturday, although it was not clear if Larfaoui was to speak about Thorpe.

After the Athens Games, Thorpe took a yearlong break to overcome "mental fatigue," then glandular fever kept him from a planned return at the 2006 Commonwealth Games in Melbourne. Minor injuries also affected his training.

Thorpe was honored at the opening ceremonies for this year's world championships.

"I have a number of mixed emotions," he told the crowd in Melbourne. "One is I really want to get back in here and swim."

The Aussie fans let out a big cheer, but Thorpe quickly set them straight.

"Not going to happen," he said, smiling and shaking his head.

Thorpe won five Olympic gold medals, 11 world titles and set 13 long-course records and 23 overall in his career.

At the 2000 Sydney Olympics, he won the 400-meter freestyle and was part of Australia's winning 400-meter and 800-meter relay teams. He also took silver in the 200 freestyle and 400 medley relay.

At the 2004 Athens Games, Thorpe won the 200 and 400 freestyle golds and the 100 bronze. He also took a silver in the 800 freestyle relay.

Thorpe followed the Sydney Olympics with his greatest performance ever. At age 18, he became the first swimmer to win six gold medals at the world championships, claiming three individual titles and taking part in three relay victories in 2001 at Fukuoka, Japan.

Thorpe set world records in all three of his solo wins: the 200, 400 and 800 freestyles. He also was part of the record-setting Australian team in the 800 free relay.