AC Milan entered the San Siro on Sunday night with a two-point lead over Inter Milan, while Atalanta were still fighting for a place in Europe. Milan's last home victory over Atalanta was in 2014, followed by four draws and three defeats.
While the first leg of the competition is slated to be played on 18-19 February and 25-26 February, the second leg will be played on 10-11 March and 17-18 March.
Sarri revealed that Ronaldo was not yet ready to take the field for the Atalanta match despite taking the field for Portugal in the International break.
Atalanta had been a thorn in Lazio's side this season, defeating them twice during the Serie A season and ruining that club's hopes of earning a spot in next season's Champions League with a 3-1 away victory earlier this month at Stadio Olimpico.
