Financial backer a new member put up (5)
I believe the answer is:
angel
'financial backer' is the definition.
(I've seen this before)
'a new member put up' is the wordplay.
'a new' becomes 'an' (I've seen this in other clues).
'member' becomes 'leg' (I've seen this before).
'put up' is a reversal indicator.
'leg' backwards is 'gel'.
'an'+'gel'='ANGEL'
(Other definitions for angel that I've seen before include "somewhere on the Northern Line" , "Seraph or cherub?" , "Old coin; theatre investor" , "Theatre backer" , "Person of beauty, purity or kindness?" .)