The 22-year-old has been linked with a number of heavyweight clubs over the past year, namely Manchester United and European champions Real Madrid.
Milinkovic-Savic is reportedly valued at £80m by Lazio, having already turned down an offer of around £72m during last summer's transfer window, and that figure is expected to grow.
Providing an update on the Serbia international's future, Kezman told Tuttomercatoweb: "There's huge interest in him from great clubs in Italy, England, Spain and France.
"I don't want to talk about numbers, but I'm sure Sergei has it in him to be the best player in Europe in the next few years. Still, we'll talk about transfers at the end of the season. Lazio, for now, are playing great football and having an important season. We're all focused on this."
Milinkovic-Savic has 11 goals and three assists in 29 Serie A and Champions League outings this term, including a couple of goals in the 3-0 win over Sassuolo at the weekend.