All but the last, playing the doctor in (6)
I believe the answer is:
almost
'all but' is the definition.
(I've seen this before)
'last playing the doctor in' is the wordplay.
'playing' indicates an anagram.
'the doctor' becomes 'mo' (medical officer).
'in' indicates putting letters inside.
'last' with letters rearranged gives 'alst'.
'alst' going around 'mo' is 'ALMOST'.
'the' is the link.
(Other definitions for almost that I've seen before include "Virtually" , "Nearly, not quite" , "Not totally" , "Well-nigh" , "As good as" .)