Exhausted old king stopping by (6)
I believe the answer is:
bleary
'exhausted' is the definition.
(thesaurus)
'old king stopping by' is the wordplay.
'old king' becomes 'lear'.
'stopping' is an insertion indicator (stopping can mean blocking a gap).
'lear' placed into 'by' is 'BLEARY'.
(Other definitions for bleary that I've seen before include "Dim" , "Misty" , "Eyes like this are dull from exhaustion" , "with tired eyes" , "Dulled with fatigue" .)