Final plans for a new-look leisure centre in Heston are expected by February, but it is likely to be at least three years before construction begins.
Builders Barratt finally reached a complex legal agreement for the project with Hounslow Council at a crunch meeting last month - nearly five years after being chosen as its preferred developer.
Architects are busy finalising changes to the internal layout of the new library and fitness facilities before submitting a formal planning application early next year.
But, even if the long-awaited project gets the go-ahead, plummeting property prices mean it could be manyyears before builders descend on the site.
The deal would see Barratt fund the new leisure centre, in the south-west corner of Heston Park, in return for permission to build homes on the site of the existing facilities in New Heston Road.
However, house prices have slumped in the last year, while building costs continue to rise, meaning the land is worth much less than the estimated £20million cost of the new centre.
Lee Dawson, the council's head of property services, told members of the Heston & Cranford area committee last Thursday that construction was unlikely to begin until at least 2011.
"There's been a lot of talk Barratt would pull out because of the credit crunch," he said.
"The reason they haven't done so is because they've invested so much time and money to reach this stage.
"At the moment the scheme's not viable because residential values have plummeted and the site's not worth £20m," he said.
"The hope is over time the value of the land will increase but we can't wait forever for the scales to balance because that could take another 10 years, during which time the leisure facilities will continue to decline.
"I don't think this scheme will be viable before 2011."
Should the scheme get the go-ahead Barratt would have until 2011 to begin construction, after which date the council would be entitled to look for another developer.
Mr Dawson added that officers were already working on a 'plan B' should Barratt fail to meet that deadline, but insisted the size of both sites would remain the same.