Weakened, has performed, holding instrument (7)
I believe the answer is:
diluted
'weakened' is the definition.
(diluting is a kind of weakening)
'performed holding instrument' is the wordplay.
'performed' becomes 'did' ('do' can be a synonym of 'perform').
'holding' indicates putting letters inside.
'instrument' becomes 'lute' (lute is a kind of instrument).
'did' enclosing 'lute' is 'DILUTED'.
'has' acts as a link.
(Other definitions for diluted that I've seen before include "Weaker" , "Watered down or attenuated." , "reduced in strength" , "Lessened the strength of a solution" .)