Foot injury initially seen by a GP, perhaps (4)
I believe the answer is:
iamb
'foot' is the definition.
(type of metrical foot in poetry)
'injury initially seen by a gp perhaps' is the wordplay.
'initially' says to take the initial letters.
'seen by' means one lot of letters go next to another.
'gp perhaps' becomes 'MB' (Bachelor of Medicine - GP is a type of doctor).
The initial letter of 'injury' is 'i'.
'i'+'a'+'mb'='IAMB'
(Other definitions for iamb that I've seen before include "Line of verse" , "Poet's foot" , "Short-long metric foot" , "Short-long metrical foot" , "Metrical unit" .)