Approach grasping old fellow? Definitely not! (2,4)
I believe the answer is:
no fear
'definitely not' is the definition.
(I've seen this before)
'approach grasping old fellow?' is the wordplay.
'approach' becomes 'near' ('near' can be a synonym of 'approach'**).
'grasping' is an insertion indicator.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'fellow?' becomes 'f' (abbreviation - of a society etc.).
'o'+'f'='of'
'near' placed around 'of' is 'NO FEAR'.
(Other definitions for no fear that I've seen before include "Very clear Five ac [REFUSAL]" , "Never" , "Far one (anag.)" , "Informally, certainly not., who's afraid" , "Definitely not (sl.)" .)