Tired, with no energy, making one cautious (4)
I believe the answer is:
wary
'one cautious' is the definition.
(I've seen this in another clue)
'tired with no energy' is the wordplay.
'tired' becomes 'weary' (similar in meaning).
'with no' suggests deleting specific letters.
'energy' becomes 'e' (physics symbol as in E=mc2).
'weary' with 'e' taken away is 'WARY'.
'making' acts as a link.
(Other definitions for wary that I've seen before include "Careful - cautious" , "Cautious - vigilant" , "Circumspect" , "James Bond villain" , "Guarded" .)