England's largest hospital trust is to call in a specialist squad to help it tackle its "biggest ever financial challenge".
Sources at Barts Health NHS Trust have told BBC London if the trust did nothing it could face being taken over by outside administrators.
The trust had planned to save £77m this financial year but after three months it is already £15m behind its target.
It is already talking about cutting about 1,000 posts.
One of its biggest problems is the huge bill it is paying for the new Royal London Hospital site in Whitechapel.
Opened in February by the Queen, it was part of a £1bn private finance initiative and paying back that PFI is costing the Trust £115m a year.
'Not in administration'
The Trust has a turnover of £1.25bn and a workforce of 15,000.
Sources told BBC London that specialist teams from the NHS Trust Development Authority would start work at the Trust on Thursday.
They will talk to all clinical groups and look at ways to save money.
Sources stressed that any changes to services would only go ahead if a strong clinical and safety case was made for them. They said care and quality were not negotiable.
They admitted though that it was possible that some services may be moved around to try to save money, but said the decision to call in outside help was essential to help get the trust "back on track".
In a statement, the trust said: "We wish to be clear that Barts Health is not in administration.
"Having not met our own financial targets for the first quarter of the financial year, we have, with immediate effect, placed ourselves in financial turnaround.
"Financial turnaround has not been imposed on us, and by taking this decision proactively and at the earliest possible opportunity, we believe we have acted responsibly to secure our long term financial viability, allowing us to continue to provide world-class healthcare to the people of east London and beyond."
A NHS Trust Development Authority spokesperson said: "They have alerted us that they have fallen behind on their financial plan in the first quarter of this year and we will work with them on the plans to recover their financial position."
The trust runs the Royal London Hospital, St Bartholomew's, Whipps Cross, Mile End, London Chest Hospital and Newham University Hospital.