Medusa's transformation may be taken for granted (7)
I believe the answer is:
assumed
'be taken for granted' is the definition.
(synonyms)
'medusa's transformation' is the wordplay.
'transformation' indicates anagramming the letters.
'medusas' is an anagram of 'ASSUMED'.
'may' acts as a link.
(Other definitions for assumed that I've seen before include "Falsely adopted" , "Put it on - without being told?" , "Took for granted" , "Taken as true; adopted" , "Took (responsibility)" .)