Les Bleus, having finished second behind winners Spain in Group I, will battle the Ukrainians in a two-legged tie for the chance to progress to next summer's finals in Brazil.
Deschamps has told his players to relax ahead of the first game on Friday in Kiev, and Mavuba feels that the quality time that France are spending together is only helping the team's preparations.
"The simple fact of being together, without distractions from the outside, can create that extra something," Mavuba told the media. "These are the most important matches we've faced in the Deschamps era."
Deschamps took charge of France after the conclusion of Euro 2012.