RIBEIRAO PRETO, Brazil (AP) -- While France's free-flowing attack is working well at the World Cup, doubts remain over the true quality of its unproven defense.
The center half pairing of Mamadou Sakho and Rapahel Varane is largely untested as they have been playing together for little more than one year.
When Sakho limped off with a sore thigh against Switzerland last Friday, France looked unsettled and conceded two quick goals in a 5-2 win in Group E.
''It didn't ruin the win for us, but we know we have to concentrate until the end,'' Varane said.
Although France has all but secured its place in the next round, better opponents could expose what is a very raw back four.
France won the 1998 World Cup and the European Championship in 2000 with a defense featuring Lilian Thuram, Marcel Desailly, Laurent Blanc and Bixente Lizarazu - widely considered the best in the world.
They had played together for years, whereas the current defense cruelly lacks such experience, with the exception of 33-year-old left back Patrice Evra.
The 21-year-old Varane has eight international appearances - five of them starting with Sakho.
When Sakho came off, Laurent Koscielny replaced him and France conceded twice in the last 10 minutes.
Varane has started just once alongside Koscielny in a 1-0 defeat against Spain in a World Cup qualifier in March last year, while France's fourth-choice center half Eliaquim Mangala has only made three international appearances.
The vulnerability of the defense is further underlined by doubts over Varane's right knee and Koscielny's temperament.
Varane, who had surgery at the end of the 2012-13 season, did well in the Champions League final win against Atletico Madrid a month ago but played only 14 league games last season.
''I've been feeling good in the last few weeks,'' Varane said. ''For the time being everything's going well and I hope it continues.''
Wednesday's final Group E game against Ecuador could be a chance for Deschamps to give Koscielny and Varane more playing time, in case they are paired together later in the tournament.
Varane missed Sunday's team training session because of gastroenteritis, while Sakho and Koscielny - who has been hampered by tendinitis in his Achilles in recent weeks - also sat it out.
Although the 28-year-old Koscielny is a regular with Arsenal, he has been in and out of the France team since making the first of his 18 appearances nearly three years ago. There are question marks about his temper, after he completely lost control and got sent off in the first leg of the World Cup playoff against Ukraine, which France lost 2-0.
With 60 caps, Evra is easily the most experienced defender and is playing in his fourth major tournament, more than any other player in the squad.
''It's good that he looks after the young players (because) we need that,'' Varane said. ''He tells us not to put ourselves under too much pressure and that we shouldn't hesitate to talk to him.''
Despite his young age, Varane exudes natural authority. He has been earmarked for a bright future ever since marking Barcelona star Lionel Messi out of the game and scoring in both legs of a Spanish Cup semifinal win two seasons ago, when he was just 19.
''I try to talk to players as much as possible, whether they're veterans or not,'' Varane said. ''I try and sort out certain tactical issues because, as a center half, I can see the whole game in front of me.''