Gambling Mecca in Grenoble (4)
I believe the answer is:
reno
'gambling mecca' is the definition.
(I've seen this in another clue)
'in grenoble' is the wordplay.
'in' indicates the answer is hidden within the clue.
'RENO' is hidden within 'grenoble'.
(Other definitions for reno that I've seen before include "American city" , "City in Nevada known for gambling and easy marriage/divorce" , "City in Nevada known for casinos and easy divorces" , "City in Nevada known for casinos and easy divorce" , "gambling centre" .)