Milinkovic-Savic believes Onana is now Inter's first-choice ahead of captain Samir Handanovic.
“I think he's an excellent goalkeeper, he has a brilliant future ahead of him. He succeeded in taking Handanovic's place, today I think he's stronger than the Slovenian," the 25-year-old declared.
Milinkovic-Savic's Serbia faces Onana and Cameroon in the World Cup tonight.
He added: “The compliments help me to have faith in myself, but the match against Brazil didn't give us any points, so I can't help but look forward."