The Croatians kick off the tournament on June 12 against hosts Brazil in the opening match.
Since he had named a 30-man provisional squad in mid-May, Kovac had to rule out four injured internationals - QPR's Niko Kranjcar, Hamburg duo Milan Badelj and Ivo Ilicevic and Ivan Strinic of Dnipro Dnipropetrovsk.
Young players such as Dinamo Zagreb goalkeeper Oliver Zelenika, currently on loan at Lokomotiva, as well as Rijeka midfielder Ivan Mocinic, both aged 21, have also found a place in the squad.
Kovac announced the squad after a friendly against Mali which Croatia won 2-1.
"We can do better than this ... players told me that they are really too tired," the 42-year-old former Croatia captain said after the warm-up in the eastern town of Osijek.
The FIFA deadline for naming squads is Monday.
The Croatia squad includes two Brazilian-born players -- forward Eduardo Silva of Shakhtar Donetsk and midfielder Sammir, both former Dinamo Zagreb key players.
Sammir, renowned for his off-the-field antics, joined Spanish side Getafe this year.
The 'Fiery Ones' (Vatreni) were to leave for Brazil on Tuesday and will play their last World Cup warm-up match on June 6 against Australia.
Croatia's Group A also includes Cameroon and Mexico.
Croatia's best result at a World Cup was third in 1998 in France, but they failed to qualify for South Africa in 2010.
Croatia squad
Goalkeepers: Stipe Pletikosa (Rostov/RUS), Danijel Subasic (Monaco/FRA), Oliver Zelenika (Lokomotiva Zagreb)
Defenders: Darijo Srna (Shakhtar Donetsk/UKR), Domagoj Vida (Dynamo Kiev/UKR), Sime Vrsaljko (Genoa/ITA), Danijel Pranjic (Panathinaikos/GRE), Vedran Corluka (Lokomotiv Moscow/RUS), Dejan Lovren (Southampton/ENG), Gordon Schindelfeld (Panathinaikos/GRE)
Midfielders: Luka Modric (Real Madrid/ESP), Ivan Rakitic (Sevilla/ESP), Mateo Kovacic (Inter Milan/ITA), Marcelo Brozovic (Dinamo Zagreb), Ognjen Vukojevic (Dynamo Kiev/UKR), Ivan Mocinic (Rijeka), Sammir (Getafe/ESP)
Forwards: Mario Mandzukic (Bayern Munich/GER), Nikica Jelavic (Hull City/ENG), Ivica Olic (VfL Wolfsburg/GER), Eduardo Da Silva (Shakhtar Donetsk/UKR), Ivan Perisic (VfL Wolfsburg/GER), Ante Rebic (Fiorentina/ITA)
FIFA World Cup: Luka Modric, Mario Mandzukic Spearhead Croatia's 23-Man Squad
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