That risk may increase pressure on Mayor of London Boris Johnson, who is also chairman of the Legacy Company, to provide extra public money for the redevelopment of the Olympic Stadium and the Olympic Park.
But the report warns that ambitious legacy plans aimed at transforming area in East London may be eclipsed by the short-term need to raise capital from high-value housing developments.
It also highlights on-going uncertainty over the cost of converting the Olympic Stadium and says the final details of the transformation of the venue have yet to be confirmed with West Ham.
West Ham were named as the ranked highest of the bids by the Legacy Company at their Board meeting earlier this week although there is still a non-football option in case a deal with the Premier League team for a 99-year lease on the £429 million ($691 million/€528 million) Stadium falls through.
"The once-in-a-generation transformation of the Olympic Park represents a huge opportunity for East London, but doesn't come without financial risk," said the Assembly's Budget and Performance Committee chairman John Biggs.
"Uncertainty over the Stadium deal as well as question marks over developer contributions both represent significant risks for the LLDC.
"We need a guarantee from the Mayor that London taxpayers will not be left to pick up the bill."
The report also highlights the potential long-term cost of transport improvements, schools, housing and health facilities not fully-funded by developers and calls on the Mayor to set out in more detail how much risk the Legacy Comapny is exposed to.
It call for Johnson to honour his pledge not to call on further contributions from council tax payers and makes a series of recommendations on a range of issues.
These include setting out the implications for Transport for London (TfL) if fares rose by inflation rather than above inflation level and ensuring plans for reducing costs from Metropolitan Police are judged against changes to policing capacity overall.
"I hope the Mayor will take on board the recommendations of our report and provide the Assembly with the information and assurances we need to endorse his budget," added Biggs.
The Mayor is expected to publish his Budget in early January 2013 and the Assembly will then consider whether to approve it following a series of public meetings.
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November 2012: Olympic Stadium may not reopen until 2016, admits Legacy chief
October 2012: West Ham must wait over Olympic Stadium move