Nick Clegg will meet with Liberal Democrat backbenchers later in a bid to secure their support for the government's embattled NHS reforms.
One Lib Dem MP, Andrew George, has already said he will not back the health and social care bill when it returns to the floor of the Commons tomorrow.
Many others are expected to abstain, leaving Mr Clegg facing a tough challenge as he seeks to win over wavering backbenchers to secure the reworked reforms.
Plans to place competition and a market dynamic at the heart of the NHS were dramatically watered down after a 'listening pause' earlier this year.
But concerns about the health and social care bill, which still seeks to introduce choice across the NHS, have been fanned by emails seen by the Observer newspaper.
They showed that health officials were considering private companies, potentially from overseas, to run up to 20 hospitals.
Health secretary Andrew Lansley dismissed the claim that the NHS would be privatised as "nothing more than ludicrous scaremongering".
The British Medical Association (BMA) has called for the legislation to be withdrawn, however, while the Trades Union Congress (TUC) has said it was "barely improved" by the Future Forum consultation.
"Neither coalition party said they would undermine the NHS in this way in their manifestos, and the government has absolutely no mandate for this toxic cocktail of competition, markets and cuts," TUC general secretary Brendan Barber said.
He called for the reforms to be challenged in the Lords, where the legislation will be scrutinised if it passes its Commons stages. Opposition from the government benches in the upper chamber could be led by Shirley Williams.
She wrote in yesterday's Observer: "Despite the great efforts made by Nick Clegg and [Lib Dem health minister] Paul Burstow, I still have huge concerns about the bill. The battle is far from over."
Mr Clegg could face a more direct challenge later this month. Former Lib Dem MP Evan Harris has called for the legislation to be debated at the party's conference in Birmingham, which gets underway in less than two weeks' time.