In an interview with Vatican Radio, Navarro-Valls also sought to reassure Catholics around the world about the pope's condition, reiterating an earlier statement that "there is no reason for alarm".
Tests had shown that the pope's respiration and heart were normal and that he had "a little fever," the spokesman said, a result of the flu that had previously caused him to cancel his usual weekly audience in St Peter's Square Wednesday.
The pope was rushed to Rome's Gemelli hospital at 10:50 pm (2150 GMT) on Tuesday with what the Vatican described as an "acute" throat inflammation and "laryngo-spasm" - a condition where one cannot catch one's breath.
Navarro-Valls said the pontiff was given "respiratory assistance" overnight but was in a stable condition by Wednesday morning, and was even preparing to say mass. He denied that he had undergone a tracheotomy, required in severe cases of laryngo-spasm, a medical term for the closure of the larynx that blocks the passage of air to the lungs.