Elite British athletes competing at the 2012 Olympics in London are set to face uncertainty over funding, says a report from the National Audit Office.
The NAO said plans to raise £100m as part of a seven-year, £700m, private sector package may be hit due to delays in fundraising and sponsor demands.
"There is a risk that raising all this money is not achievable," it warned."
But British Olympic Association chairman Colin Moynihan insisted on Thursday there will not be a problem.
"The British Olympic Association believes that the Prime Minister will deliver on his promise made in 2006 to secure the full £600m for the British team," he said.
"This is despite the concerns raised by the NAO report that the Government is entering a crowded market place in their attempt to raise part of the promised funding for our Olympic and Paralympic athletes from the private sector."
Moynihan's statement comes after the NAO suggested "UK Sport should avoid distributing too high a proportion of the extra funding to those sports with no medal potential".
After the 2004 Athens Olympics, when the British team returned nine gold medals, UK Sport adopted a "no compromise" policy of focusing funding on sports and athletes with a real chance of success.
Our ambitions are dependent on the full funding package being available
Chief executive of UK Sport, John Steele
As a result, 16 sports are now receiving money from UK Sport for the first time, and only Olympic football and tennis are not given funding.
"Should there be a significant funding shortfall, UK Sport is currently working on a range of contingency plans which it will finalise and discuss with sports following the Beijing 2008 Games," the NAO confirmed.
"It is already too late, however, for UK Sport to protect the full funding it proposes for those sports it expects to win medals in 2012 if the worst case funding scenario should materialise."
Yet Moynihan claims that would go "completely against our principles and the spirit on which the 2012 bid was based".
He added: "There is an expectation that the host nation will field competitive teams in all sports and the BOA is committed to this aspiration, which would see British athletes competing in sports such as basketball and volleyball for the first time in a number of years.
"The inspiration of seeing British athletes in these team competitions would help to deliver the large scale participation increases which the Government is committed to."
Chief executive of UK Sport, John Steele, welcomed the NAO review and said: "We are pleased with the key findings of this report, which gives us real confidence that we are on the right track in terms of our strategy and approach.
"I would like to thank the NAO for their valuable insights and we will take on their thoughts and recommendations and make sure they help us in our continual drive to deliver our twin ambitions for 2012: medal success at the Games and the lasting legacy of transformed and sustainable elite sporting system.
"We recognise too the risks they highlight - in particular the fact that our ambitions are dependent on the full funding package being available."