Real Madrid midfielder Modric has backed his country to match their achievement at the 1998 World Cup, where the team reached the semi-finals.
"This is an important game for us and I'm very proud of what we've achieved so far. But we need to forget everything that has gone before," the 32-year-old said.
"It will be a stern test for us but it's high time this generation gets over this particular hurdle which have not managed to do since 1998.
"We are full of confidence and we've shown during the group stage that we play as a team but we have to do it again."
Croatia are the third-highest scorers so far in the tournament after scoring seven goals in their opening three matches.