The plan is expected to include a debt for equity swap or rights issue, although the latter would be a challenge after recent share price falls to their lowest point since 1984.
In a trading statement covering third quarter performance this morning, the troubled contractor said its expected year-end net debt to be worse than expected, up to £625m-£650m.
This deepened due to additional cash outflows on Energy from Waste as well slow payments in certain Middle Eastern markets.
Shares fell a further 8% to 32p in early trading.
White warned that the construction division would report a loss in the second half and that profits at the RMD Kwikform business, within the equipment services division, would be down due to delays in major infrastructure projects.
Despite these set-backs, she said Interserve would deliver a significant improvement in operating profit at year end and the Fit for Growth programme remained on track to deliver its target of £15m savings in 2018.
“Following the successful completion of the refinancing in April, the business has traded robustly in some challenging markets and continued to win significant new contracts,” she said.
“The ‘Fit for Growth’ programme is delivering material cost savings and a simpler and more effective business structure. Overall we remain on track to deliver a significantly improved financial performance this year in line with our plan.
“The board remains focused on positioning the group for long-term, sustainable success.”
White said that this meant closing out and exiting the Energy from Waste business and reducing debt and putting a strong long-term capital structure in place.
She added: “To this end we will announce a deleveraging plan for the group early in 2019.”
The board is working with its advisers to look at all options to deliver the optimum capital structure for the business.
This process includes options to bring new capital into the business and progressing the disposal of non-core businesses, she said.