He's on his own concerning clues' solution (7)
I believe the answer is:
recluse
'he's on his own concerning clues' solution' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'he's on his own concerning' is the wordplay.
I cannot quite see how this works, but
'on' could be 're' (regarding) and 're' is found in the answer.
'concerning' could be 'c' and 'c' is found in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for recluse that I've seen before include "Solitary individual" , "Solitary figure" , "Eremite" , "One seeking solitude" , "Anchorite" .)