Prepare to fight graduate in US city, having lost head (8)
I believe the answer is:
embattle
'prepare to fight' is the definition.
(to embattle is to prepare for a battle)
'graduate in us city having lost head' is the wordplay.
'graduate' becomes 'MB' (someone with a Bachelor of Medicine degree).
'in' is an insertion indicator.
'us city' becomes 'seattle' (city in Washington, USA).
'having lost head' means to remove the first letter.
'seattle' with its initial letter taken away is 'eattle'.
'mb' inserted within 'eattle' is 'EMBATTLE'.
(Other definitions for embattle that I've seen before include "Arrange in readiness for conflict" , "Make ready to fight; belt mate (anagram)" , "Fortify" , "strengthen the defence" , "add strength" .)