Positive results against Turkey on Sunday and the Czech Republic could render Croatia's clash with the defending champions irrelevant to their hopes of escaping the group, and Modric is confident of their chances.
Having played his club football in Spain for the last four years, Modric is well aware of the threat posed by Vicente del Bosque's team.
The Real Madrid star told Marca: "I think the group is really difficult. Firstly we play Turkey, then Czech Republic and finally Spain.
"I think the first match will be key. If we manage to win, our path to the knockout stage will be easier.
"It will be hard as always against Spain, one of the best teams in the world. I hope we have already booked our ticket to the next stage by then."
He added: "Our first goal is to advance past the group stage and I feel we are very capable of accomplishing it."
Modric enjoyed a solid season in 2015-16, flourishing under the management of Zinedine Zidane as Madrid won the Champions League, but a strong performance at a tournament with Croatia remains a career ambition for the 30-year-old.
He said: "I want to win or make a deep run with Croatia into a major tournament and I still have yet to win La Liga.
"I feel the utmost pride every time I wear it given our history. I always look forward to playing for my national team, especially at a major tournament."