Donor is treated at home (7)
I believe the answer is:
indoors
'home' is the definition.
(I've seen this before)
'donor is treated' is the wordplay.
'treated' is an anagram indicator.
'donor'+'is'='donoris'
'donoris' is an anagram of 'INDOORS'.
'at' acts as a link.
(Other definitions for indoors that I've seen before include "Within a building" , "Covered" , "Not outside" , "Within the four walls" , "Within house" .)