Inter is reported to have already reached an agreement with the German club to sign Lazaro for €22million.
And the 23-year-old, who has contributed directly to 16 goals in the past two Bundesliga seasons, arrived in Milan on Sunday to complete the move.
Speaking outside Lazaro's hotel in the Italian city, agent Federico Pastorello told TuttoMercatoWeb: "He's very happy. He needs his rest now, as the medical is set for very early tomorrow morning."
Austria international Lazaro previously spent five years in Salzburg's first team, before making the switch to Hertha in 2017.