The Real Madrid midfielder suffered a foot injury in his side's 3-1 loss to Brazil in the FIFA World Cup opener.
But while he is yet to return to training despite scans clearing him of serious damage, Modric is expected to face Cameroon at the Arena de Amazonia in Manaus.
Asked how likely Modric was to play, Croatia doctor Boris Nemec told reporters: "Greater than 90 per cent.
"Therapy is common, ice and stretching, but we cannot force him."
The hot and humid conditions in Manaus troubled England and Italy players during their clash on Saturday, with no mid-half water breaks permitted.
Nemec said fluids were the key to overcoming the difficult conditions.
"The temperature and humidity are exhausting for players. They must drink lots of fluids," he said.
