The new Secretary of State for Business, Enterprise and Regulatory Reform is to have surgery later today to remove a kidney stone.
Peter Mandelson is the first gay man to sit in the Cabinet since 2001.
A BERR spokesman said the procedure would take place today after the minister underwent tests in hospital over the weekend.
This morning the 54-year-old former EU Commissioner attended the first meeting of the government’s new National Economic Council, the Prime Minister’s “new approach to coordinating economic policies across government.”
A spokesman for the Business Department said: “Over the past few days, Peter Mandelson has been experiencing some kidney pain.
“Hospital tests yesterday confirmed that there is a small stone. This will be dealt with by the normal procedures later today.”
Mr Mandelson’s return to British politics after more than seven years of out of the Cabinet was the most eye-catching appointment in Gordon Brown’s reshuffle.
They were regarded as sworn enemies since Mr Mandelson chose to back Tony Blair over Mr Brown for leader of the Labour party in 1994.
Less than a year after his appointment as Secretary of State for Trade and Industry in 1998 Mr Mandelson was forced to resign after it emerged he purchased his west London home with an interest-free loan from a fellow Labour MP whose business dealings were under investigation by the department.
Many thought his career was over but just ten months later Tony Blair made him Secretary of State for Northern Ireland.
Mr Mandelson was an effective negotiator and his efforts to bring peace to the province were praised on both sides of the political divide.
However, in January 2001 he was implicated in another scandal after it was alleged he intervened to try and get British citizenship for an Indian businessman who was being investigated for corruption.
Mr Mandelson resigned again. He has been the UK’s appointee to the European Commission since November 2004.
The Prime Minister has defended his decision to appoint Mr Mandelson.
At a press conference on Friday Mr Brown said their relationship was “very good.”
“Peter Mandelson has proved himself as Commissioner in the last few years as someone of great distinction,” he said.
“What I have decided is what I believe is in the national interest. It is in the national interest that we bring together all the people who can serve us to the best effect.
“If you have got someone with unrivalled experience in international business issues, someone who is respected by business for what he has done and who has built a reputation over these last few years as someone who can get things done, then if the British government can benefit from that it is the right decision and you set aside all the issues of the past in the national interest, and that is what we are doing today.”
While Mr Mandelson’s return is audacious, it is not without its risks.
Seen as a highly divisive figure by many in his own party, his pechant for intrigue and publicity could be a toxic combination, as it was at the start of the Labour administration.
Over the weekend the Business Secretary let it be known he phoned Tony Blair for advice after he was offered his third job in the Cabinet, while he denied that at he had rubbished the Prime Minister just a few weeks ago at a dinner with the Shadow Chancellor George Osborne.
Tory leader David Cameron admitted on BBC television yesterday that the phrase ‘a Mandelson’ is used within his party’s inner circle to describe the length of time before meeting Mr Mandelson and him criticising the Prime Minister.