Doctors are being replaced by less qualified nurses to provide out-of-hours services.
People who become ill at weekends or at night are being treated by nurses and emergency care practitioners after GPs handed over responsibility to Primary Care Trusts (PCTs).
Sussex PCTs are outsourcing the work to private companies for cover.
Politicians fear the move places will add pressure on under-threat accident and emergency services across the county.
Lewes MP Norman Baker said: "The major worry is that if this system isn't robust more and more people will go to A&E for more experienced health practitioners at a time when hospitals are potentially closing. It's another unwelcome pressure.
"PCTs are also short of cash so there's also a question of the number of staff these companies are employing."
All the PCTs in Sussex are now using the out-of-hours firms - some as many as three to cover each area.
Three years ago, the Government renegotiated contracts with GPs which allowed them to opt out of providing care at weekends and evenings for only a £6,000 cut in their £100,000 average salaries.
PCTs took over responsibility but many claim they have struggled to offer the same quality of service.
The House of Commons Public Accounts Committee last month described the handover as "shambolic".
Katherine Murphy, of the Patients Association, said the changes were being driven by poor financial management, rather than good patient care.
But the cash-strapped PCTs insist doctors are not always needed.
Brighton and Hove City PCT, facing a £389,000 shortfall, said it was actually increasing its payment to out-of-hours provider South East Health.
A spokeswoman said: "There has been a shift towards using more nurses where traditionally it was a doctor led service and the PCT would see that as appropriate because nurses and doctors have different skills.
"Nurses are very good at face-to-face assessment and telephone triage.
"About 60 per cent of out of hours activity is completed over the phone but doctors are always available."
East Sussex Downs and Weald PCT also use South East Health - a private company with six "bases" across the coast from Brighton to Rye - as well as another firm called On Call Care.
They are also replacing GP shifts with nurses, though insist only doctors will do home visits.
A contractual agreement between the PCTs and the providers stipulates one qualified doctor is always available.
West Sussex PCT uses three different firms.
The Argus contacted the organisation but by yesterday morning, managers were still unable to tell us whether nurses were being used in place of doctors.
Other than for one of the companies, Thamesdoc - which is not cancelling GP shifts - communications manager Linda Benny said she did not know.
Madeleine Mayhew, communications manager for East Sussex, said: "When you think of a doctor's practice sometimes it is appropriate you see a practice nurse and sometimes a doctor.
"Similarly, if it's something a nurse can deal with you will talk to a nurse out of hours. There's a skills mix. Nurses are used as appropriate, particularly in the initial telephone contact.
"There certainly is a shift in that skill mix so less doctors are being used but there are doctors there to do consultations and home visits as needed.
"They are the local GPs that are part of the service."
Have you called out-of-hours services and been treated by a nurse rather than a doctor? How was the treatment you received? Leave your comments below.
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