De Sciglio, 26, picked up a muscular problem during Saturday's 4-3 Serie A win for the Italian champions over Napoli.
Mancini had already been forced into another change after Juve captain Giorgio Chiellini, 35, tore a ligament in his right knee, an issue that will keep the defender out for around six months.
The 103-times capped Chiellini had made way for Lazio centre-back Francesco Acerbi.
Italy will play Armenia in Yerevan on Thursday, then visit Finland next Sunday.
Goalkeepers: Gianluigi Donnarumma (AC Milan), Pierluigi Gollini (Atalanta), Alex Meret (Napoli), Salvatore Sirigu (Torino)
Defenders: Leonardo Bonucci (Juventus), Danilo D'Ambrosio (Inter Milan), Emerson Palmieri (Chelsea/ENG), Alessandro Florenzi, Gianluca Mancini (both Roma), Armando Izzo (Torino), Luca Pellegrini (Cagliari), Alessio Romagnoli (AC Milan), Francesco Acerbi (Lazio)
Midfielders: Nicolo Barella (Inter Milan), Bryan Cristante, Lorenzo Pellegrini (both Roma), Jorginho (Chelsea/ENG), Stefano Sensi (Inter Milan), Marco Verratti (Paris Saint-Germain/FRA)
Forwards: Andrea Belotti (Torino), Federico Bernardeschi (Juventus), Federico Chiesa (Fiorentina), Stephan El Shaarawy (Shanghai Shenhua/CHN), Ciro Immobile (Lazio), Lorenzo Insigne (Napoli), Kevin Lasagna (Udinese)