Man perhaps, shortly saying 'I will' (4)
'man perhaps' is the definition.
(I've seen this before)
'shortly saying i will' is the wordplay.
'shortly' means to remove the first letter.
'saying' indicates a 'sounds like' (homophone) clue.
'i will' becomes 'ill' (I've seen this before).
'ill' is a homophone of 'aisle'.
'aisle' with its initial letter taken away is 'ISLE'.
(Other definitions for isle that I've seen before include "being impossible without water", "eg Man, Wight", "Capri for one", "Land amid water", "Small region of land".)