A proposal to level the track where Olympic hero Jessica Ennis trains and replace it with a new athletics facility and a rugby ground has been announced less than a fortnight after the decision to sacrifice Sheffield's Don Valley Stadium.
Backers of the new scheme claim it could create more than 900 jobs.
But former sports minister and Sheffield Labour MP Richard Caborn, who announced the proposal in the city, admitted the current £40 million estimated cost was still a "back of a fag packet" estimate.
He said the plan was to access a range of funding opportunities but stressed it would be funded by a Sheffield City Council subsidy.
The decision to close and demolish the £29 million Don Valley Stadium, in Sheffield, as part of council cost-cutting measures was announced earlier this month.
Mr Caborn said the new proposal to replace the stadium will be the "biggest Olympic legacy project outside of London".
He said it would involve an upgrade of an existing athletics facility half a mile away and building a stadium for both codes of rugby on part of the footprint of the current Don Valley Stadium.
Labour-run Sheffield City Council announced the closure of the Don Valley Stadium on March 1 as part of £50 million of savings it must make next year. It said the £700,000 it spent subsidising the facility each year was unsustainable as the stadium was running at a loss.
The council said it subsidises every visit by more than £5 and it requires major repair and maintenance work - totalling around £1.6 million.
At a press conference, council leader Julie Dore said: "We are determined not to let this Government defeat this city. We are still ambitious and we still will find solutions for Sheffield and the people of Sheffield. This is an opportunity our city will hopefully take forward."