At midnight, muddled heads get injured (6)
I believe the answer is:
gashed
'injured' is the definition.
('gashed' can be similar in meaning to 'injured')
'at midnight muddled heads' is the wordplay.
'at' means one lot of letters go next to another.
'midnight' becomes 'g'.
'muddled' is an anagram indicator.
'heads' with letters rearranged gives 'ashed'.
'g'+'ashed' is 'GASHED'.
'get' is the link.
(Other definitions for gashed that I've seen before include "Wounded" , "Deeply cut" , "Cut open" .)