I left aspirin, ordered for injury (6)
I believe the answer is:
sprain
'injury' is the definition.
(sprain is a kind of injury)
'i left aspirin ordered' is the wordplay.
'left' is a deletion indicator.
'ordered' is an anagram indicator.
'aspirin' with 'i' removed is 'asprin'.
'asprin' is an anagram of 'SPRAIN'.
'for' is the link.
(Other definitions for sprain that I've seen before include "Minor muscular injury" , "sign of strain" , "Wrench, the ankle say" , "Pulled muscle" , "Wrench a joint" .)