Need month off for getting better (2,3,4)
I believe the answer is:
on the mend
'getting better' is the definition.
(on the mend means recovering from illness)
'need month off' is the wordplay.
'off' indicates an anagram.
'need'+'month'='needmonth'
'needmonth' with letters rearranged gives 'ON THE MEND'.
'for' acts as a link.
(Other definitions for on the mend that I've seen before include "Becoming better in health" , "Regaining health" , "Improving in health" , "Making recovery" , "Recovering from an injury or illness" .)