Health managers admitted on Thursday that the Royal Cornwall Hospitals Trust is more in debt than first thought.
The trust reported a deficit of £8.1m in March
In March the trust, which runs the Royal Cornwall Hospital in Truro, reported a deficit of £8.1m and announced that 300 jobs would go.
The trust now says the overspend is greater but will not release a figure and declined to comment on speculation it could be as high as £18m.
Auditors are looking at the accounts and will report in two weeks.
Price Waterhouse Cooper is working with the trust to produce a plan which will help it pay off the debt and help to balance the books in the future.
St Ives Lib Dem MP Andrew George said: "I was sceptical that the deficit was as little as £8.1m at the time the announcement was made in March.
"Sources I have heard from suggest we're talking about something which is quite substantially more."