Officials at the Vatican say ill health has forced Pope John Paul to cancel his weekly general audience.
The Pope suffers from Parkinson's Disease and arthritis
The 83-year-old pontiff is reported to be suffering from intestinal problems.
Officials said the ailment was not serious.
But correspondents say the Pope has cancelled his general audience at short notice only a handful of times during his 25-year papacy.
The Vatican's number two, Secretary of State Angelo Sodano, presided over the audience in place of the pontiff, reading the speech and welcoming pilgrims.
The Pope spoke to the pilgrims by a telephone link from his summer residence near Castel Gandolfo near Rome.
In a frail voice, the pontiff said how sorry he was not to be there, his words trailing off towards the end.
Pope John Paul has a busy schedule for October, when he is due to mark the 25th anniversary of his election on October 16 1978, followed by the beatification of Mother Teresa of Calcutta on 19 October.
Renewed concerns were raised about the Pope's health during a visit to Slovakia earlier this month.
During the trip, his aides had to take over many of his speeches and sermons.
Observers said during public engagements he was clearly in pain.
The pontiff's speech has become extremely slow and slurred as a result of Parkinson's disease.
Although he has been in ill health for some time, his appearance in Slovakia indicated a marked deterioration in his state, correspondents said.
The Pope underwent an operation in 1992 to remove a large tumour from his intestine, which proved to be benign.
He suffered more intestinal problems in 1995 and a year later was operated on for appendicitis.