Tees is ready: solver reportedly unprepared! (9)
I believe the answer is:
impromptu
'unprepared' is the definition.
(impromptu means improvised or unprepared)
'tees is ready solver reportedly' is the wordplay.
'tees is' becomes 'I'm' (where the crossword setter is 'Tees').
'ready' becomes 'prompt' (similar in meaning).
'solver' becomes 'you' (the person solving the clue!).
'reportedly' shows a homophone (sound like).
'you' sounds like 'u'.
'im'+'prompt'+'u'='IMPROMPTU'
(Other definitions for impromptu that I've seen before include "Unplanned; composition" , "Ad hoc: spontaneous-sounding musical piece mastered by Schubert" , "Spontaneously, off the cuff" , "Extemporaneous speech" , "piece by Chopin, perhaps" .)