Spain take on tournament debutants Cape Verde in Atlanta on Monday as they begin their World Cup campaign in Group H alongside Uruguay and Saudi Arabia.
Yamal, 18, and Williams, 23, missed the end of their respective domestic seasons after both suffering hamstring injuries which left Spain fans worried about their chances of featuring this summer.
However, addressing the media on Sunday, De la Fuente confirmed the pair should be okay to start the clash against Cape Verde where is side are firm favourites.
"The good news is that Lamine is in perfect condition," the coach said. "He's arrived at this point in the state in which we wanted him to be.
“He's fine, just like Nico (Williams) and Victor (Muñoz). They're all available, although some won't play the entire game."
Neither Yamal nor Williams played any part in World Cup warm-up friendlies against Iraq and Peru but after returning to training over the past week, it looks like the pair have returned to full fitness.
Yamal recorded 24 goals and 18 assists for Barcelona in the 2025-26 season and will make his World Cup debut on Monday night as he leads the next generation of players who will shine at the tournament for years to come.
Cape Verde sit 67th in the FIFA's rankings, and they have never previously competed at the World Cup as an independent nation. Spain are firm favourites and 3 points look almost certain for De la Fuente and his side.