Long-suffering doctor's client (7)
I believe the answer is:
patient
I believe this is a double definition.
'long-suffering' is the first definition.
('patient' can be similar in meaning to 'long-suffering')
'doctor's client' is the second definition.
(I've seen this before)
(Other definitions for patient that I've seen before include "Sufferer" , "one of interest to medics?" , "One receiving medical care" , "one receiving medical treatment" , "Not easily provoked" .)