Man about to drop off (3)
I believe the answer is:
nod
'drop off' is the definition.
(I've seen this in another clue)
'man about' is the wordplay.
'man' becomes 'Don' (Don is an example).
'about' says the letters should be written in reverse.
'don' back-to-front is 'NOD'.
'to' acts as a link.
(Other definitions for nod that I've seen before include "even Homer sometimes does" , "Indicate 25 [YES]" , "OT land" , "Drowse" , "Land of exile" .)