A new number to be put up shortly (4)
I believe the answer is:
anon
'shortly' is the definition.
(I've seen this before)
'a new number to be put up' is the wordplay.
'a new' becomes 'an' (I've seen this in other clues).
'number' becomes 'no' (abbreviation for 'number').
'to be put up' says the letters should be written in reverse.
'no' written backwards gives 'on'.
'an'+'on'='ANON'
(Other definitions for anon that I've seen before include "devoid of credit" , "Soon, in a little while" , "Incognito (abbrev)" , "Presently - unattributed" , "Shortly; unknown" .)