Single-digit growth worried one in the end (7)
I believe the answer is:
toenail
'single-digit growth' is the definition.
(digit as in finger or toe)
'worried one in the end' is the wordplay.
'worried' indicates an anagram.
'in' is an insertion indicator.
'the end' becomes 'tail' (tail is a kind of end**).
'one' is an anagram of 'oen'.
'oen' going into 'tail' is 'TOENAIL'.
(Other definitions for toenail that I've seen before include "woman in labour" , "may need this cut?" , "Keratinous growth" , "One of ten" , "Footplate, perhaps" .)