The 14-year-old daughter of King Felipe will be tested for coronavirus like other pupils in her class at the Santa María de los Rosales school in Madrid.
The king and Queen Letizia will continue their royal duties for the moment, a spokesman for the royal household said, as Spain struggles to control a surge in coronavirus cases.
Eight million Spanish children returned to school last week but some have closed or classes been sent home after pupils tested positive for COVID-19, while authorities in Galicia delayed the start of term by a week for pupils aged 14 to 18.
Spain reported 4,708 new coronavirus infections on Friday, bringing its cumulative total to 566,326, the highest in western Europe, as its total COVID-19 death toll rose to 29,747.