Less productive apprentice runs away (6)
I believe the answer is:
Here is my best explanation:
'less productive' is the definition.
'apprentice runs away' is the subsidiary indication.
'apprentice' becomes 'learner' ('learner' can be a synonym of 'apprentice').
'runs' becomes 'r' (cricket abbreviation).
'away' suggests deleting specific letters.
'learner' with 'r' removed is 'leaner'.
(Other definitions for leaner that I've seen before include "Less productive", "less productive", "One with an inclination", "less corpulent?", "Less fat", "With less fat", "Thinner, with less fat" and "less bulky".)