Suffered head injuries without initial sign of concussion (5)
I believe the answer is:
ached
'suffered' is the definition.
('ache' can be a synonym of 'suffer')
'head injuries without initial sign of concussion' is the wordplay.
'injuries' indicates an anagram (I've seen 'injury' mean this).
'without' indicates putting letters inside ('without' can be similar in meaning to 'outside').
'initial sign of concussion' becomes 'c' (I can't justify this - if you can you should believe this answer much more).
'head' is an anagram of 'ahed'.
'ahed' enclosing 'c' is 'ACHED'.
Can you help me to learn more?
(Other definitions for ached that I've seen before include "Throbbed" , "Hurt" , "Yearned" , "caused discomfort" , "Did long" .)