Kovacic was expected to play a big part for Group H leaders Croatia against third-placed Norway in Euro 2016 qualifying in Zagreb on Saturday.
But the sought-after Inter player, who has been linked with Premier League outfit Liverpool this week, will miss the qualifier in the Croatian capital.
"I saw Kovacic. He has a cruciate knee ligament injury," Nemec told 24sata.hr.
"He still feels a lot of pain and there is absolutely no chance he'll be able to play against Norway."
Croatia top the group ahead of Italy on goal difference after four matches, while Norway are a point off the pace.
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