The Deputy Prime Minister will be among the senior politicians and religious leaders presented to Benedict XVI by the Queen at Holyroodhouse Palace in Edinburgh, at the start of the historic state visit. But the Prime Minister's name has not been included on the official schedule, distributed to journalists on Monday.
This would leave the Government represented at the reception by the Liberal Democrat leader, who while married to a Roman Catholic has stated that he is "not an active believer".
Downing Street said it could not confirm whether or not the Prime Minister would attend, and added that he will have a private meeting with the Pope during the four-day tour of Scotland and England.
It would surprise many if Mr Cameron did not attend the welcome ceremony, given his efforts to make sure the Pontiff's visit passes off smoothly following a series of early setbacks.
The Prince of Wales, known for his interest in religion and spirituality, will also be conspicuous by his absence when Benedict XVI is greeted by the Queen, the Duke of Edinburgh and senior politicians.
The heir to the throne will also miss the Pontiff’s address to hundreds of members of “civil society” at Westminster Hall, London, who will include religious leaders and former Prime Ministers.
A source at Clarence House said: “The Prince didn’t request a meeting. He met the Pope at the Vatican last year.”
However his decision is likely to be seen by some Roman Catholics as a snub, particularly as the two men are known to have opposing views on issues such as contraception.
Following the pomp of the official welcome next Thursday, the Pontiff will travel through the streets of Edinburgh in the Popemobile so that those who do not have tickets for the open-air Mass at Bellahouston Park will be able to see him.
The following evening, Londoners will be able to see the famous customised vehicle as the Pope travels from Lambeth Palace, where he is meeting the Archbishop of Canterbury, to Whitehall.
On the Saturday evening, before a prayer vigil in Hyde Park, the Popemobile will travel down the Mall past Buckingham Palace. Security is likely to be high as opponents of the visit are planning a rally in central London that day.
Lord Patten of Barnes, appointed by the Prime Minister to oversee the papal visit, told the BBC’s Hardtalk programme that he was “not at all” worried about protests from atheists, secular campaigners and clerical abuse victims.
He said: “I would be amazed if there weren’t some protests. This is a free society, it’s the sight and noise of freedom when people protest.”
But he added that “the numbers won’t be huge” and that the protestors will “behave in a reasonable way”.