Wimpey is favourite to buy Laing Homes, and it has been reported in the past month that the firm was conducting due diligence.
Analysts had predicted the deal would be announced this week when the companies reported their interim results. But Wimpey chief executive Peter Johnson failed to mention it, and Laing said it was under no pressure to sell its housebuilding division.
The City's disappointment led to Laing's shares immediately falling 9p to 151p; Wimpey's share price dropped 3.5p.
An analyst said: "We thought Laing would have announced it on Monday with their results, but they didn't; then Wimpey didn't even mention it at all. Something must have happened because the talk all last week was of a deal being announced with the results."
Analysts said Laing was under pressure to sell its housing arm to help ease debt and fund its PFI business. But Laing is holding out for about £300m for the business, which contributed more than 60% to the group's operating profit for the six months to 30 June.
Laing reported a group pre-tax profit of £13.5m compared with a £49.7m loss for the same period in 2001. Last year's deficit largely stemmed from its struggling construction business, which was sold last October to Ray O'Rourke. Despite the recovery, Laing was had to meet interest payments of about £20m on the debts racked up by its construction business.
Laing Homes' sales rose to 648 units from 567 for the same period last year. Operating profit fell from £23.9m to £22.5m as margins were reduced from 13% to 10.5%.
At the group's PFI investment business, which would become Laing's main business if the homes division was sold, operating profit rose 19% to £13.6m.
Meanwhile, Wimpey reported a 121% jump in pre-tax profit from £38.9m to £86.3m after the acquisition of Alfred McAlpine Homes last year. Turnover rose 44% from £706.7m to £1.02bn.
Wimpey said trading in the UK and USA remained strong. In the UK, the firm's average selling price rose 19% to £140,000.