Thousands of protesters from around the country are preparing to march against proposals to scrap a "high performing" hospital's A&E department and downgrade its maternity ward.
Under Government plans, Lewisham Hospital in south-east London would see its emergency department - which recently completed a £12 million revamp - replaced with an "urgent care" ward and its maternity services turned into a midwife-led unit.
It is part of a radical overhaul proposed by special administrator Matthew Kershaw in response to nearby South London Healthcare NHS Trust (SLHT) going into administration after it started losing around £1.3 million a week.
But SLHT - which runs three hospitals in the capital and was the first NHS trust to collapse - does not have responsibility for Lewisham Hospital.
Campaigners say a "successful and well-run" hospital is in danger of being sacrificed due to the neighbouring trust's failure. They also believe closure of Lewisham Hospital's A&E department would have a knock-on effect which could lead to the demise of other wards.
Health Secretary Jeremy Hunt is due to make his decision on the proposals by February 1.
Protest group Save Lewisham Hospital said it is expecting more than 15,000 people from all over the country to be at Saturday's march. Helen Tattersfield, a local GP and chairwoman of Lewisham's Clinical Commissioning Group, said the group has been "overwhelmed" by the support so far.
She said: "It just highlights that this a national issue. This is the first time the Government has put in place its 'failure regime' for an NHS trust - and the proposed solution is to destroy services at a successful and high performing neighbouring trust.
"The 'failure regime' is set to be used many more times across the UK, so if the Government can close down Lewisham Hospital then no successful hospital in the country is safe."
The march will go past Lewisham Hospital and end with a festival in nearby Mountsfield Park. Speakers will include radio presenter Nick Ferrari, who has previously spoken on his show about how Lewisham Hospital saved his son's life.