(ANSA) - Florence, September 4 - AS Roma defender Federico Balzaretti and Cagliari defender Davide Astori will not be playing in Italy's upcoming World Cup qualifiers against Bulgaria and Malta due to leg injuries, the national team's doctor Enrico Castellacci said on Tuesday. "They are not serious injuries, but (the players) need a precise length of time to recover and so they will not be available for the games against Bulgaria and Malta," he said. Azzurri coach Cesare Prandelli called up AC Milan's Francesco Acerbi to take Astori's place in the squad. Instead midfielder Daniele De Rossi, who is suffering from a mild ankle sprain, could make it onto the pitch as his condition is deemed less serious. Meanwhile Milan forward Giampaolo Pazzini missed a training session on Tuesday due to a problem with his right knee but Castellacci said he was already undergoing treatment and should be able to rejoin the group shortly. On Monday Prandelli said Inter Milan striker Antonio Cassano would not be playing in the two qualifying matches as he needed time to improve his "physical fitness". Italy will face Bulgaria in Sofia on Friday in their first qualifier for the 2014 World Cup in Brazil and will host Malta in Modena four days later.