The Prince of Wales made the comments while in South Yorkshire to visit communities affected by flooding.
"He's being looked after very well in hospital," he said. "At the moment, that's all we know."
The 98-year-old Duke of Edinburgh entered the hospital Friday but neither his ailment nor his condition have been specified.
"When you get to that age things don't work so well," Prince Charles added.
News reports had also said Prince Philip was in good spirits, but he's expected to remain hospitalized for at least part of this week.
It is not yet known if Prince Philip will be well enough to spend Christmas with Queen Elizabeth II at their Sandringham estate. He missed the royals' annual Christmas Day trip to church last year.
While Prince Philip recuperated Sunday, the queen attended church at St. Mary Magdalene in Sandringham with the Countess of Wessex.
Prince Philip's hospitalization is the latest in a series of health challenges. In 2011, he was hospitalized with infections in 2012 and 2017 and underwent hip replacement surgery in 2018.