Construction firm Balfour Beatty has turned down a £1bn offer from John Laing for its public private partnership (PPP) portfolio.
Balfour said its PPP contracts, which include long-term agreements to run projects such as schools and hospitals, were worth far more than the offer.
The company said that the loss of its PPP business would have an impact on its remaining operations.
Balfour shares plunged in September after the firm issued a profit warning.
The offer from the John Laing Infrastructure Fund "falls significantly short" of the value of the PPP portfolio, Balfour said.
"The directors' valuation of the PPP portfolio stood at £1.05bn, as at 28 June 2014," the company said.
"However, the group's targeted approach to selling individual assets as each investment matures, combined with the current and expected future strength of the market, leads the board to conclude that the realisable value of the PPP portfolio continues to be substantially in excess of the current directors' valuation," it added.
The company's shares closed 15.3% lower on the day it issued its profits warning in September, compounding concerns over the UK's biggest construction group.
Balfour Beatty said there would be a further shortfall of £75m this year in its UK construction services division, following two earlier profits warnings this year.
The company appointed accountants KPMG at the end of September to review the contract portfolio.
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