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.
'Will Cristiano Ronaldo and Neymar extend their contracts in Saudi Arabia? We play a facilitating job, but it’s down to the players and the clubs to decide' Saudi Pro League chief reveals how talks will work for out-of-contract duo
Nations League: Who are the ITV commentators and pundits for England vs Republic of Ireland?
