Man is struggling to accept one — like himself? (6)
I believe the answer is:
simian
'himself?' is the definition.
I can't tell whether this definition defines the answer.
'man is struggling to accept one' is the wordplay.
'struggling' indicates an anagram.
'to accept' means one lot of letters goes inside another.
'one' becomes 'i' (Roman numeral**).
'man'+'is'='manis'
'manis' is an anagram of 'smian'.
'smian' going around 'i' is 'SIMIAN'.
'like' is the link.
(Other definitions for simian that I've seen before include "Resembling an ape or monkey" , "Monkey, say," , "Like an ape or monkey" , "Primate" , "Ape; apelike" .)