Both Brazilians have failed to make a positive impact at Juve since their summer arrivals and are being blamed for the club's current crisis.
But Dunga insists they're "victims" of Ferrara's playing system.
He told Corriere dello Sport: "Juve have ruined Diego and Melo.
"They are victims, not perpetrators, they must be played in their true roles.
"Amauri also must rediscover his scoring form."