Support for musician needing no introduction (6)
I believe the answer is:
assist
'support' is the definition.
(assisting is a kind of supporting)
'musician needing no introduction' is the wordplay.
'musician' becomes 'bassist' (I've seen this before).
'needing no introduction' means to remove the first letter.
'bassist' with its first letter taken off is 'ASSIST'.
'for' acts as a link.
(Other definitions for assist that I've seen before include "Work as a subordinate" , "Expedite" , "Understand by instinct" , "Help to make" , "benefit" .)