Small piece, not genuine, about learner (5)
I believe the answer is:
flake
'small piece' is the definition.
'not genuine about learner' is the wordplay.
'not genuine' becomes 'fake' (I've seen this before).
'about' indicates putting letters inside.
'learner' becomes 'l'.
'fake' placed around 'l' is 'FLAKE'.
(Other definitions for flake that I've seen before include "Split into thin pieces" , "Small piece of snow" , "A little snow" , "Sliver" , "Flat thin fragment" .)