Director Sergio (5)
I believe the answer is:
'director sergio' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for leone that I've seen before include "Sergio ___ , Italian film director d. 1989" , "Sierra ___ (West African country) - Sergio ___ (film director)" , "Sergio --, spaghetti western director" , "Sierra -, W. Afr. state" , "African rhino" .)