Treatment applied to man's right leg tendon (9)
I believe the answer is:
hamstring
'leg tendon' is the definition.
'treatment applied to man's right' is the wordplay.
'treatment applied to' indicates anagramming the letters (the letters must be processed or treated).
'mans'+'right'='mansright'
'mansright' is an anagram of 'HAMSTRING'.
(Other definitions for hamstring that I've seen before include "Tendon behind the knee" , "Tendon at back of knee" , "Thwart, severely restrict" , "Tendons at back of the knee" , "Cramp the style of" .)