The Pope is to break with tradition this year and celebrate Midnight Mass at 10 p.m., instead of midnight, Sky News reported.
The decision was taken two months ago to "ease the Pope's fatigue at a time when there are many ceremonies and commitments" during Christmas holidays, said Vatican spokesman the Rev Frederico Lombardi.
There was no reason to worry about 82-year-old Benedict XVI's health, the spokesman said.
It was just that Vatican aides decided to "stretch out his strength" and the pontiff agreed, he explained.
On Christmas Day at noon, Pope Benedict will read his Urbi et Orbi - to the city and the world - Christmas message from the main balcony of St Peter's Basilica.
Benedict's predecessor, John Paul II, always celebrated the Christmas Mass at midnight, even in his final years.