Loner managed to enlist (5)
I believe the answer is:
enrol
'to enlist' is the definition.
(I've seen this before)
'loner managed' is the wordplay.
'managed' indicates an anagram.
'loner' anagrammed gives 'ENROL'.
(Other definitions for enrol that I've seen before include "Sign up (member)" , "Loner (anag.)" , "Join up, sign on" , "Enter" , "Register (as member)" .)