Reason for going to press witness: he’s worn out (14)
I believe the answer is:
newsworthiness
'reason for going to press' is the definition.
(newsworthy means worthy of being printed)
'witness he's worn out' is the wordplay.
'out' indicates an anagram (out can mean wrong or inaccurate).
'witness'+'hes'+'worn'='witnesshesworn'
'witnesshesworn' with letters rearranged gives 'NEWSWORTHINESS'.
(Other definitions for newsworthiness that I've seen before include "What items must have to be reported" , "Gripping quality of story" .)