British cycling has signed its own sponsorship deal with Sky
The government will not cover a £79m sports funding gap ahead of the 2012 Games but has announced plans to step up the drive for private sponsors.
Culture Minister Andy Burnham said he was confident the cash would be raised and Team GB's success in China was the best "springboard" for the drive.
UK Sport was promised £600m including £100m from the private sector - but that has proved difficult to raise.
It has been cut to £79m as more money is expected to come from the lottery.
There have been concerns that UK athletes would face funding cuts before the 2012 Games in London because of difficulties raising money.
No sponsors have yet been signed up, but the £100m needed from sponsors has been reduced to £79m. The government says this is because, under the terms of the new National Lottery licence, more money will be raised for good causes like sport.
This week British Olympic Association chairman Lord Moynihan had called on Mr Brown to make up the shortfall from government coffers and "honour that commitment".
On Wednesday Mr Burnham, the secretary of state for culture, media and sport, announced a sponsorship drive called Medal Hopes, to involve local, regional and national businesses in sponsorship.
It could include "naming rights" of some of the Olympic venues after the 2012 Games has finished, he added.
But the scheme will not be able to use the Olympic and London 2012 brands like the Olympic rings.
"It's a £79m challenge. We have the best possible springboard and momentum from Beijing and I am absolutely confident that we will realise this goal," Mr Burnham.
But he would not say the government would step in to cover the money if it was not found saying to do so would be "to say we are not going to have a private fund-raising scheme".
"But we are planning for the full funding commitment, the commitment to funding of athletes will be met. It would be ridiculous to create any uncertainty."
The Conservatives accused the government of "raiding grassroots sports budgets" by taking extra lottery money and said it should have started raising the money earlier.
Shadow culture secretary Jeremy Hunt said: "In January the then culture secretary categorically promised the House of Commons there would be no more lottery raids to pay for their Olympics budget miscalculations.
"Six months later that promise has been torn up. Every time the lottery is raided, less money goes into grassroots sport, yet this is the only way we will secure a legacy for everyone from the 2012 Olympics."
The London organising committee and the British Olympic Association are both looking for private sector backers and some individual sports have their own agreements.
Mr Burnham admitted it was a "crowded marketplace" but said the Medal Hopes scheme would open up opportunities for local sponsors.