Ring doctor about card game (5)
I believe the answer is:
ombre
'card game' is the definition.
(I've seen this before)
'ring doctor about' is the wordplay.
'ring' becomes 'O' (letter resembling a ring).
'doctor' becomes 'MB' (Bachelor of Medicine, Medicinae Baccalaureus).
'about' becomes 're' (regarding).
'o'+'mb'+'re'='OMBRE'
(Other definitions for ombre that I've seen before include "Old card game (from the Spanish for "man")" , "Shaded" , "Tricky game" , "Card game, the name derived from the Spanish for man" , "Card-game for three; rob me (anag.)" .)