The initial estimate for staging the Games was £2.35bn
The Olympic Delivery Authority (ODA) has said it cannot guarantee that all £2bn National Lottery money taken to fund London 2012 will be returned.
It is hoped profits from land sold after the Olympic Games will reimburse National Lottery funds.
But, asked if money will be available, ODA chairman John Armitt told the Commons Public Accounts Committee: "I would not guarantee anything".
Land and assets in the Olympic Park are to be sold off after the Games.
However, it is uncertain what the future value of the land will be.
At a hearing looking at preparations for the London Games, Edward Leigh, chairman of the Public Accounts Committee (PAC), told Mr Armitt : "The Lottery has given up £2bn to good causes to you. It is absolutely essential they get some of the money back.
"You cannot possibly guarantee they will get the money back? It is possible the Lottery would not get any money back."
Mr Armitt, in charge of Olympic build and infrastructure, replied: "I would not guarantee anything."
But he said there would be "development gains" after the Games.
Jonathan Stephens, the culture department's permanent secretary, said the aim is for the Lottery to get a share of the profits from the development and regeneration of the Olympic Park in Stratford, east London, after 2012.
He told the MPs: "This is a long-term investment and development programme. Over that sort of scale these sorts of investment are realisable but it is a long-term development programme.
Mr Stephens added the Olympic project has weathered "one of the worst economic downturns in recent decade".
The cost of the Olympic project has trebled from original estimates, to £9.3bn.