The creature, a duck, is in some trouble (5)
I believe the answer is:
moose
'the creature' is the definition.
(type of animal)
'a duck is in some trouble' is the wordplay.
'a duck' becomes 'o' (resembles zero - 'duck' in cricket).
'is in' is an insertion indicator.
'trouble' indicates an anagram.
'some' is an anagram of 'mose'.
'o' put inside 'mose' is 'MOOSE'.
(Other definitions for moose that I've seen before include "Large northern deer" , "North American deer" , "beasts" , "US deer with enormous antlers" , "Ungulate" .)