Casillas and Alonso will face the former world player on Wednesday and while both showered praises on their club team-mate, Alonso emphasised on the work ethic and philosophy that Spain have followed so far.
"There is no anti-Ronaldo plan," Alonso said. "We always play with the same idea, regardless of our opponent, even though we do study them. We try to be as close as we possibly can, as together as possible," Alonso, who scored both the goals in Spain's quarter-final win over France, said.
"We are assured in how we want to play, how to work together, regardless of who we play against. The coach gives us freedom and that's gotten us this far, and we will continue in that manner," he added.
Casillas praised the quality of Ronaldo and described him as the best player in the world along with Lionel Messi, but he feels the 27-year-old Portuguese winger is yet to strike his best form in the tournament.
"I don't think Cristiano is at his best right now because he had an incredible season at Real Madrid; games, goals and records. Cristiano is, along with Messi, the best player in the world," Casillas said.
Spain right-back Alvaro Arbeloa is likely to halt Ronaldo's run on the left wing, but Spain are not going to let him tackle alone.
Spain defensive midfielder Sergio Busquets was well aware of the threat posed by Ronaldo and urged his side to work together to keep the Real Madrid star quiet on the left flank.
"We all know what a great player Cristiano is. He'll spend a lot of time on Arbeloa's side, but you need to work together as a team to stop a player like him," Busquets said.
Pass maestro Xavi Hernandez, however, warned Spain about threats by other players like Nani and Raul Meireles. But said Arbeloa will get all the support needed to stop Ronaldo break free.
"We have a great full-back in Arbeloa, who is among the best out there defensively speaking. We'll try to cover for him, to make sure Ronaldo doesn't settle and we don't let him turn," Xavi said.