Last week, the GMC said EU doctors working in the UK, including locums, will be required to take part in revalidation in exactly the same way as UK doctors.
But out-of-hours providers said the workload involved may put off some EU doctors.
Mary Jones, director of clinical and operational services for South East Health, said revalidation would 'complicate the process' for EU doctors.
She said: 'It will be somewhat more problematic for EU doctors than for UK doctors, but we welcome it as a way of strengthening the amount of assurance we have in their ability to do the job.'
Tony Snell, medical director of Harmoni, said: 'Those that purely come for a couple of sessions and just for money might well be put off.'