Pope John Paul may not be able to speak for months after undergoing a throat operation early yesterday.
Catholics around the world are asking how long a man in the Pontiff's condition can continue to run the church.
Church leaders themselves are divided, with some suggesting retirement may be theonly solution.
Suffering a relapse of his breathing problems, the Pope underwent a tracheotomy, which pierced a small opening in his neck and windpipe so air could flow directly into his lungs.
The Pope's speech had already been made very difficult by Parkinson's disease.
When and if he will be able to speak again normally is the big question.
"He can possibly survive this, but he would certainly have a very prolonged recovery, be very debilitated and very deconditioned," said Dr Barbara Paris, chair of geriatrics and vice-chair of medicine at Maimonides Medical Centre in New York.
"With a tracheotomy you can only speak with very great difficulty, if at all."
While some in the church said the Pope could govern by communicating to aides without speaking, his condition clearly signalled a new and perhaps final phase in the papacy.
Several weeks ago, the Pope missed Ash Wednesday services for the first time since his 1978 election. It looks highly likely he will now miss most or all of the Holy Week and Easter celebrations next month.
Popes usually rule until they die but advances in modern medicine mean people can be kept alive through sicknesses which, decades ago, would have killed them.
No clear regulations exist for the possibility that a Pope may be incapacitated or unable to talk.
There have been unconfirmed reports over the years that the Pope has prepared a resignation letter, to be used in case he becomes unable to carry on.
