The warning came as the 14 February deadline approached for bids for funding through the prime minister's Challenge Fund for extending access.
As GP went to press, groups of practices and CCGs across the country were finalising bids for a share of the £50m fund announced by David Cameron in October 2013. But GP has learned of at least one bid threatened by fears over capacity and future funding, and another submitted despite similar concerns.
LMC leaders reported scepticism among GPs about the fund, which aims to expand the number of practices opening 8am-8pm, seven days a week.
Opening the scheme to bids in December, NHS England deputy medical director Dr Mike Bewick said the funding for nine pilot sites would help address demand from patients for more convenient services.
But GPs feared pilots would be launched without adequate workforce and practices left to fund the extra operating hours themselves when pilot funding runs out.
One bid by practices across three CCG areas in Berkshire was at risk of being scrapped ahead of the deadline, because of GP concerns. Berkshire West CCG Federation chairman Dr Rod Smith said the bid could collapse because practices feared there were not enough GPs to support it, and worries over long-term funding.
'There's probably enough in the Challenge Fund, but you don't want to be left high and dry,' he said.
Wessex LMCs chief executive Dr Nigel Watson said while the scheme was a good idea, non-recurrent funding could cause problems. 'Practices may be reluctant to invest time and effort setting up services, only to be forced to withdraw them,' he said.
Dr Smith suggested money being taken out of PMS funding could be used to make the pilots sustainable.
GP has learned of other bids across the country. A GP federation in North East Lincolnshire has bid for funding for a seven-day opening pilot, while GPs in Hyndburn, Lancashire, are bidding to open at weekends.
Bids are being sent for review by NHS England area teams, then will be assessed by a national panel. Pilots go live in April.