The Government wants to open up the healthcare market to extend patient choice and is keen for social enterprises to get involved.
But Dr Richard Lewis, senior policy fellow at the King's Fund, said there was a danger that large, for-profit companies would snap up contracts before smaller social enterprises had time to get to grips with the changes.
He said he was concerned that the Social Enterprise Fund - which will give grants and loans to social enterprise ventures - would not be established until 2007.
"We've made the point that the Social Enterprise Fund is too far off in the distance," said Dr Lewis.
"There's a sense of urgency here that needs to be reflected in the timetable that's been put in place by the Government.
"We're not seeing progress - the Government has made the right sort of noises about the timetable, but if there isn't rapid access to that fund then the stable door may close after the horse has bolted."
Last year, the Government set up a task force, including Victor Adebowale of Turning Point and Jo Williams of Mencap, to help voluntary sector groups to contract with local health commissioners.
Then the White Paper on health and social care, published this January, set out a blueprint for a new Social Enterprise Unit and associated fund under the aegis of the Department of Health.
But Dr Lewis's report, Social Enterprise and Community-Based Care, published last week, stressed the need for focused, urgent action for social enterprises.
He told Third Sector that commissioners needed "hard and fast guidance" to avoid duplicating legal structures and frameworks that would complicate matters for new groups.
"Rather than all these nascent organisations going out and hiring their own lawyers, why can't one unit come up with a set of models that supplies all the information needed to make a reasoned decision?" he asked.
"Many of the nascent social enterprise organisations I've spoken to aren't aware of any help on offer."