Les Bleus, having finished second in Group I, will face the Ukrainians in a two-legged tie with the winner advancing to next summer's finals in Brazil.
"I already have complete confidence in Dede (Dider Deschamps) and his men," Pires told reporters. "It's an important match, but if they can stay focused and respect their opponents, they should be able to book a ticket for Brazil.
"I'm very confident. Friday's match is crucial in terms of confidence and being in a strong frame of mind for the return leg in Paris. I'm right behind them."
The first leg takes place in Kiev on Friday, before the return match in Paris on Tuesday.