Nocturnal creature needs attention following an illness (3,4)
I believe the answer is:
Here is my best explanation:
'nocturnal creature' is the definition.
'ant bear' can be an answer for 'creature' (ant bear is a kind of creature). I'm not sure about the 'nocturnal' bit.
'attention following an illness' is the wordplay.
'attention' becomes 'ear' (ear is a kind of attention).
'following' means one lot of letters go next to another.
'illness' becomes 'tb' (TB is an example).
'ear' after 'antb' is 'ANT-BEAR'.
'needs' acts as a link.
(Other definitions for ant bear that I've seen before include "Beat thoroughly", "Another term for aardvark", "Aardvark" and "beast".)