The Italy Under-21 side lost Roberto Piccoli and Antonino Gallo to injury, but brought in Caleb Okoli, Lorenzo Lucca and Samuele Mulattieri.
The Azzurrini opened their European Under-21 Championship qualifying campaign with a comfortable 3-0 win over Luxembourg.
Atalanta striker Piccoli and Lecce left-back Antonino Gallo pulled out of the training retreat due to injury.
Coach Paolo Nicolato has therefore called up another three players for the upcoming game with Montenegro on Tuesday.
They are Cremonese forward Okoli, Pisa striker Lucca and Crotone hitman Mulattieri.
It is the first Under-21 call-up for the latter two, while Okoli had been initially named in the squad last week.
Italy Under-21 squad:
GK: Marco Carnesecchi (Cremonese), Alessandro Plizzari (Milan), Alessandro Russo (Alessandria);
D: Raoul Bellanova (Cagliari), Riccardo Calafiori (Roma), Andrea Cambiaso (Genoa), Andrea Carboni (Cagliari), Gabriele Ferrarini (Perugia), Matteo Lovato (Atalanta), Caleb Okoli (Cremonese), Andrea Papetti (Brescia), Lorenzo Pirola (Monza), Iyenoma Destiny Udogie (Udinese);
M: Marco Brescianini (Monza), Jacopo Da Riva (Spal), Nicolò Fagioli (Juventus), Filippo Ranocchia (Juventus), Samuele Ricci (Empoli), Nicolò Rovella (Genoa), Sandro Tonali (Milan);
F: Matteo Cancellieri (Hellas Verona), Lorenzo Colombo (Spal), Lorenzo Lucca (Pisa), Samuele Mulattieri (Crotone), Eddie Salcedo (Inter), Kelvin Yeboah (Sportklub Sturm Graz)