De la Fuente told a pre-match press conference he had no concerns about his players finding the requisite energy before heading off on holidays.
"They're all fine. No one is going to let us down. We're going to give it a whirl tomorrow," he said.
"I think my team have peaked at the best moment of the season. Motivation overcomes everything."
De la Fuente took over as Spain coach after their last-16 elimination at the World Cup last November, and he now has a chance to win a title in only his fourth game in charge.
"What gives recognition are the titles, but what matters is the previous work. The title puts the varnish on the work," he said.
"To get to a final is a privilege. If you leave everything out there on the pitch, there can be no frustration afterwards. Of course, we want to win, not for me but to make our supporters happy."
Croatiague, however, will be a tricky opponent for Spain, the coach added.
"I see it as a very even contest, each team has their own strong characteristics but we have both shown that today we are the two best teams in Europe.
"We would like to win the game inside the 90 minutes. They have more experience, and that half hour (of extra time) is vital in terms of experience. A calm head sets the tone, and I think Croatia are also very strong physically."