Decosse, 30, won silver at the Beijing Olympics and is a triple world champion. She is the favourite to take the women's 70-kilogram category on Wednesday but faces serious competition from other judokas including Maria Portela of Spain, who said she has spent considerable time studying Decosse's matches on video to come up with a winning strategy against her.
Decosse shrugged off the expectation she will take gold. "That I am the favourite does not mean that I am going to win, but I will do everything for it," she said. "I have trained very hard, but there are no guarantees."
Still, Decosse said her previous accomplishments have given her a boost, citing her last world championship. "I am confident but not cocky," she said.
After Japan, France has won the most Olympic judo medals of any country.
Since the Olympic judo competition began on Saturday, there have been plenty of surprises, including several top seeds crashing out in their first bouts.
Japanese fighter Haruka Tachimoto may be a contender, though it will be her Olympics debut. Like many of her compatriots, she specializes in throwing her opponents from an upright position, favouring a technique that combines footwork and an upper body twist to knock her opponent backwards.
In the men's 90-kilogram division, many expect Greek Ilias Iliadis to take gold. Iliadis won gold in a lower weight division at the Athens Olympics but came 20th at Beijing in the division he's now fighting. Still, he is a double world champion and is top-ranked in his category.
Iliadis will face tough competition from other favourites including Masashi Nishiyama of Japan, Dilshod Choriev of Uzbekistan and Cuban Asley Gonzalez.
On Tuesday, South Korea and Slovenia won their first judo gold medals of the London Games.
In the men's 81-kilogram division, Kim Jae-bum of South Korea improved on the silver he won in Beijing by winning the gold. To do it, he beat the man he lost to in Beijing: Ole Bischof of Germany.
Bischof said Kim was now stronger and faster and said the right man had won. After their final, the two hugged.
Kim is the current judo world champion. His gold added to South Korea's judo medal tally; teammate Cho Jun-ho won a bronze in the lightweight men's division earlier this week.
The bronze medals were won by Ivan Nifontov of Russia and Antoine Valois-Fortier of Canada.
American Travis Stevens fought several grueling matches to make it to the semifinal, but lost to Bischof. Valois-Fortier then edged him out for the bronze.
In the women's division, Urska Zolnir of Slovenia won the women's 63-kilogram class, defeating Xu Lili of China in a combative final where both fighters were almost constantly on the offensive. Zolnir managed to throw Xu once in the match's first minute, which was ultimately enough to win.
Zolnir, 31, was one of the oldest competitors in the division. She won a bronze at the 2004 Athens Games and came seventh at Beijing four years ago. She doesn't expect to be competing for much longer and probably will retire before the next Summer Games in Brazil. "You won't meet me in Rio," she predicted.
The bronze medals were won by Yoshie Ueno of Japan and Gevrise Emane of France.
Ueno's bronze was the only Japanese medal of the day, despite the country's judokas being viewed as favourites going into the competition. So far, Japan has won one gold, two silver and two bronze medals, a disaster for the country that invented the sport.
"We still have tomorrow," she said.