Macho man unable to open reading desk (4)
I believe the answer is:
ambo
'reading desk' is the definition.
(I've seen this in another clue)
'macho man unable to open' is the wordplay.
'macho man' becomes 'rambo' (film character played by Sylvester Stallone).
'unable to open' means to remove the first letter.
'rambo' with its initial letter removed is 'AMBO'.
(Other definitions for ambo that I've seen before include "Early form of pulpit" , "Where the preacher stood" , "Old reading-desk" , "Early Christian pulpit" , "Raised pulpit" .)