His agreement about to wilt (3)
I believe the answer is:
sag
'wilt' is the definition.
(I've seen this in another clue)
'his agreement about' is the wordplay.
'about' indicates the answer is hidden within the clue (the clue goes around or about the answer).
'SAG' can be found hidden inside 'his agreement'.
'to' is the link.
(Other definitions for sag that I've seen before include "Spinach as used in Indian cookery" , "Subsidence" , "Give in the middle" , "Give way under pressure" , "Lose energy" .)