Blood deficiency (7)
I believe the answer is:
anaemia
'blood deficiency' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for anaemia that I've seen before include "complaint of blood" , "Llama relative, its wool" , "Blood deficiency condition" , "Blood disorder -- ie I am Ana (anag)" , "cause of pallor" .)