It was feared the 28-year-old had fractured a bone during Croatia's 3-1 loss to Brazil in the tournament's opener on last Thursday. (Agencies)
He spent the following day in a Sao Paulo hospital before scans cleared the Real Madrid midfielder of serious damage.
At a press conference on Tuesday, Croatia coach Niko Kovac revealed Modric was certain to play at the Arena Amazonia stadium on Wednesday.
"Luka is going to be 100 percent fit. He did well in training. There are no problems and he will be with us in Wednesday's clash," Kovac said.
Having lost their opening matches, both Croatia and Cameroon must avoid defeat to remain alive in the tournament.
But Kovac vowed his side would attack from the outset in the Amazonian city of Manaus in a bid to secure victory.
"They (Cameroon) may play for a draw, but we want to win," he said.
"We want to play our game. They are a strong team that is high in quality, but we want to impose our own style of play,” he added.
“If we were to play in the same way we played against Brazil, I do not see why we can't progress (to the knockout phase). I know there is no such thing as a free lunch, but we will fight and I am confident we can win,” Kovac said.
Croatia have been buoyed by the return of striker Mario Mandzukic from suspension. The 28-year-old Bayern Munich forward could not hide his eagerness to help his team on Wednesday.
"This is maybe one of the most important matches most of us have played in," Mandzukic said.
"We are ready and personally I can't wait for it to start,” he added.
It was feared the 28-year-old had fractured a bone during Croatia's 3-1 loss to Brazil in the tournament's opener on last Thursday.