One's worked diligently, it's inferred? The opposite! (7)
I believe the answer is:
implied
'inferred? the opposite' is the definition.
'implied' can be an answer for 'inferred?' (thesaurus). I'm not sure about the 'the opposite' bit.
'one's worked diligently' is the wordplay.
'one's' becomes 'I'm' ('one is' is a formal way of saying 'I am').
'worked diligently' becomes 'plied' (to ply at a trade is to work hard at it).
'im'+'plied'='IMPLIED'
'it's' is the link.
Can you help me to learn more?
(Other definitions for implied that I've seen before include "Stated indirectly" , "I limped in hinted or suggested way" , "Suggested; not explicit" , "Insinuated, hinted" , "Understood" .)