Modric announced this week he would be leaving Real Madrid with his contract expiring at the end of June.
Mijatovic said on El Larguero: "I'm a little sad about the news. Everything has a beginning and an end. One of the greatest is leaving.
"Who's going to wear the number 10 now? What's that number 10 going to do? Will he be able to do what Luka did? There are 1,500 questions right now.
"I don't remember Real Madrid having another player as complete as Luka Modric."
World Cup a target
He also said: "I know Luka very well.
"He's the age he is, and Modric wanted to stay at Real Madrid for another year and perform well for the 2026 World Cup with Croatia.
"Luka Modric accepted two years ago that he wouldn't be an undisputed starter, but year after year he's played a lot... more than expected."
On where Modric will pop up next, Mijatovic declared: "In football, anything is possible, but knowing Modric, I don't think he'll go to an exotic league. Luka wants to compete and perform well, and the top five leagues can provide that for him.
"In any case, he's not going to be in a hurry, and wherever he goes, he wants to remain competitive and important