Mandzukic missed his nation's 3-1 loss to Brazil in the FIFA World Cup opener due to suspension but is back for the Group A match in Manaus on Wednesday.
Kovac said the Bayern Munich man's return was a big boost for Croatia, who like Cameroon desperately need a win.
"I am very glad for Mario Mandzukic to be with us, his skills are well known," Kovac told a news conference.
"Any coach would be satisfied to have such a player in their ranks. I know he will inject some energy into this match and lead us to victory, I hope.
"As far as the match is concerned we know what it means to us and Cameroon. We've come here to play football and win three points because it means so much to us.
"Let's not dwell on the maths, let's focus on the game and the three points."
After Mexico held Brazil to a 0-0 draw on Tuesday, Croatia and Cameroon are four points behind the duo.
Kovac said it was matches against Cameroon and Mexico that were his team's focus leading into the tournament.
"We came here to the World Cup knowing that we would be playing Brazil," he said.
"We thought we could get something out of the match but realistically speaking games two and three mean more to us because these are competitors for second place."
Kovac said the pitch at the Arena Amazonia, where England lost 2-1 to Italy, was better than he expected.
Spray paint was used on the pitch before the England-Italy clash due to patchiness and dryness.
"The pitch is quite good, I heard stories it wasn't good. Initially it looked tough out there and hot, but when they started sweating it was better," Kovac said.
"The conditions are what they are, we have to accept them, we are not fishing for excuses."
