The Duke of Edinburgh was initially checked into King Edward VII's Hospital Thursday with a heavy cold and has been undergoing a medical assessment.
A consultant will make the final determination whether the royal official should remain hospitalized or be discharged, the BBC reported Saturday.
Philip's illness prompted him to miss a memorial service for Sir Edmund Hillary, who gained fame for being one of the first people to reach Mount Everest's summit.
The 86-year-old prince's hospital stay has been labeled a precaution rather than an emergency visit by royal officials, the BBC said.
"Whenever people hear that someone has been admitted to hospital, particularly when they're in their mid-80s, it's understandable that they are concerned," Dr. John Moore-Gillan, a London lung specialist, told the BBC of Philip's condition.
"But the overwhelming majority of people with chest infections are going to make a rapid and complete recovery and that is particularly the case when they are generally fit and healthy for their age."