Puccini's so right about upcoming composer (7)
I believe the answer is:
rossini
'composer' is the definition.
(Italian composer Gioachino Rossini)
'puccini's so right about upcoming' is the wordplay.
'about' indicates the answer is hidden within the clue (the clue goes around or about the answer).
'upcoming' shows that the letters should be reversed in order (in a down clue coming up is backwards).
'inissor' is hidden within 'puccinis so right'.
'inissor' backwards is 'ROSSINI'.
(Other definitions for rossini that I've seen before include "Italian scorer" , "opera producer" , "Composer of 'The Barber of Seville' and 'William Tell'" , "whose barber was in Seville" , "he scored regularly" .)