The Prince of Wales is discussing his wedding date with Royal aides after the Vatican said that the Pope's funeral would take place on the same day.
Prince Charles and Mrs Parker Bowles will marry in a civil ceremony
Clarence House earlier said the Royal ceremony at Windsor's Guildhall and the church blessing, would proceed regardless of any clash on Friday.
But it added the wedding plans remained "sensitive to other events" and that it would continue to assess the situation.
Charles cut short his holiday to attend a London Mass for the Pope on Monday.
Camilla Parker Bowles would also attend the service at Westminster Cathedral, Clarence House said.
The prince and Mrs Parker Bowles are to marry in a civil ceremony and will then attend a church service in St George's Chapel at Windsor Castle.
A 45-minute religious church blessing led by the Archbishop of Canterbury will follow.
BBC Royal correspondent Nicholas Witchell says the Archbishop of Canterbury "would almost certainly have attended the Pope's funeral".
He says the diary clash puts the Church of England leader in a "very difficult position".
Lambeth Palace said it would be inappropriate to comment at this stage.
The Queen and the Duke of Edinburgh have already announced they will not be attending the civil ceremony but will be at the blessing.
Before it was announced the Pope's funeral would be on the same day, a spokeswoman for Clarence House said: "If the funeral were to take place on Friday it would not affect the wedding.
Downing Street said "relevant discussions" were taking place over whether the prime minister attends the Royal Wedding or the Pope's funeral on Friday.
Before the funeral was confirmed a spokesman said: "The prime minister spelt out his view of the Pope's life and his huge contribution to the world in the statement that was issued on Saturday night and the words he spoke himself yesterday.
"That reflects the significance that the prime minister gives to the Pope's death."
The BBC's Norman Smith says Number 10 is wary of trying to attend both events, given the risk of delays and unforeseen problems travelling between the two.
"It would appear Number 10 are waiting to see if the Palace decide to delay the wedding before making any final decision," he says.
Tony Blair has already delayed calling a general election as a mark of respect for Pope John Paul II.
He will instead attend the same service as Prince Charles at Westminster Cathedral later on Monday.
It earlier emerged Mrs Parker Bowles will receive the title of the Princess of Wales, but has chosen not to use it.
Constitutional affairs minister Christopher Leslie, in a written parliamentary answer to Labour MP Andrew Mackinlay, will formally announce Mrs Parker Bowles' title on Monday.
Asda has made replicas of Mrs Parker Bowles' engagement ring
A spokeswoman for the Department of Constitutional Affairs said: "She will be the Princess of Wales, but she will not use the title. Clarence House have said this all the way through."
The Palace has already confirmed that Mrs Parker Bowles wants to be known as the Duchess of Cornwall.
Her title will become Princess Consort when the Prince is crowned king.
Meanwhile, supermarket chain Asda began selling silver and ubic zirconia replicas of Mrs Parker Bowles' engagement ring on Monday.
It said 30% of the 2,500 rings had already sold.