Macmahon announced the downgrade last month, followed by the departure of chief executive Nick Bowen last week, as it reviews its Hope Downs 4 Rail Earthworks contract in Western Australia.

Mr Bowen is to be replaced by chief operating officer Ross Carroll. Macmahon Holdings chairman Ken Scott-Mackenzie on Tuesday said the board shared the extreme disappointment of shareholders.

''I would like to apologise to you for the recent earnings downgrade and the effect this has had on the value of your investment in Macmahon,'' he said. AAP