"We have 23 lions in the squad," Srna told a news conference before training at the Gdansk Stadium on Sunday.
"We have no complex, no fear of Spain, we don't overly respect them. All the world will be watching and we've already shown that we can play with the big teams and win."
"You look at Lionel Messi, he doesn't play so well for Argentina as he does for Barcelona, the same with Cristiano Ronaldo, he doesn't play so good for Portugal," Srna said.
"But Croatian players, we play much better for the national team than we do for our clubs. We are ready to fight."
With a 3-1 victory over Ireland and a 1-1 draw with Italy here in Poland, they have again shown the "strong mentality" that coach Slaven Bilic believes will hold them in good stead against a mighty Spanish side on Sunday.
"This current generation has something special," former West Ham United and Everton defender Bilic, who will stand down after six years in charge after the tournament, said.
"The energy is perfect. We play our best when we play better against the best teams and this is the biggest match for this generation. It's going to be difficult against Spain but when we have the ball we'll attack with self confidence.
"I think we'll have some surprises for the Spanish team."
"I don't really want to waste any more words talking about it," he said. "Everyone in the competition and in Italy can be calm. It's a part of the brain that we don't have.
"If the final score is 2-2, that's it, it's football. If it's 7-7, then that would be strange."
Bilic said Spain had shown "two faces" at the tournament so far but added that his team would learn from Italy's performance when they drew 1-1 with the Spaniards in the group opener.
They will thus play with two strikers in Nikica Jelavic and Mario Mandzukic, the tournament's joint top scorer with three goals. Jelavic trained on Sunday after recovering from a fever.
