The 42-year-old has named goalkeeper Oliver Zelenika, striker Duje Cop and midfielders Marcelo Brozovic, Ivan Mocinic and Mario Pasalic in his provisional 30-man squad for the finals.
Nikola Kalinic was left out to make room for Cop, who has scored 22 goals in 32 games for Dinamo Zagreb this season.
Kovac's squad features star names in the shape of Luka Modric, Ivan Rakitic and Mario Mandzukic, and the coach already has his final 23-man group in mind.
"I have in my head which 23 players will go to Brazil, but we left some space," said Kovac. "Everyone has a chance to prove themselves.
"Mocinic played a superb season. When he was in the Under-21s he was a little restrained, but every day he is getting better
"It is similar with Pasalic and Brozovic and they will one day be the mainstays of the team.
"I personally explained why Leon Benko, Kalinic and Hrvoje Milic were not invited."
Defender Josip Simunic was unavailable for selection after his 10-match ban for "discriminatory behaviour" was upheld by the Court of Arbitration for Sport.
Croatia face Brazil, Cameroon and Mexico in Group A of the World Cup.
Squad in full:
Goalkeepers: Stipe Pletikosa (Rostov), Danijel Subasic (Monaco), Oliver Zelenika (Lokomotiva).
Defenders: Igor Bubnjic (Udinese), Vedran Corluka (Lokomotiv), Dejan Lovren (Southampton), Danijel Pranjic (Panathinaikos), Gordon Schildenfeld (Panathinaikos), Darijo Srna (Shakhtar), Ivan Strinic (Dnipro), Domagoj Vida (Dynamo Kyiv), Sime Vrsaljko (Genoa).
Midfielders: Marcelo Brozovic (Dinamo), Milan Badelj (Hamburg), Mateo Kovacic (Inter), Niko Kranjcar (QPR), Ivan Mocinic (Rijeka), Luka Modric (Real Madrid), Mario Pasalic (Hadjuk), Ivan Rakitic (Sevilla), Jorge Sammir Cruz Campos (Getafe), Ognjen Vukojevic (Dynamo Kyiv)
Strikers: Duje Cop (Dinamo), Eduardo (Shakhtar), Ivo Ilicevic (Hamburg), Nikica Jelavic (Hull City), Mario Mandzukic (Bayern Munich), Ivica Olic (Wolfsburg), Ivan Perisic (Wolfsburg), Ante Rebic (Fiorentina)
