Patients are "less likely" to give favourable feedback to doctors that have been awarded a primary medical degree in a non-European country, it is claimed.
Furthermore, colleagues of doctors working in a GP capacity are also less likely to give positive feedback.
In a study published in the British Medical Journal, researchers from the Peninsula College of Medicine and Dentistry claim they identified "systematic bias" in the assessment of doctors' professionalism by patients and colleagues.
They warn official assessments by regulatory bodies should "be interpreted carefully".
Researchers based their analysis on surveys undertaken by the colleagues and patients of 1,065 doctors.
Collectively, the doctors returned completed questionnaires from 17,031 colleagues and 30,333 patients.
The study found non-white patients and those reporting that not seeing their 'usual doctor' are more likely to give "less favourable" feedback
Doctors practising as a psychiatrist were also less likely to receive positive feedback from patients.
Researchers noted a doctors' colleagues are less likely to give a favourable review if they received their degree from any country other than the UK or South Asia.
"Systematic bias may exist in the assessment of doctors' professionalism arising from the characteristics of the assessors giving feedback, and from the personal characteristics of the doctor being assessed," said the researchers.
"In the absence of a standardised measure of professionalism, doctor's assessment scores from multisource feedback should be interpreted carefully, and, at least initially, be used primarily to help inform doctor's professional development."