Tops up, just a little (4)
I believe the answer is:
spot
'a little' is the definition.
(thesaurus)
'tops up' is the wordplay.
'up' is a reversal indicator (in down clue: letters go upwards).
'tops' backwards is 'SPOT'.
'just' acts as a link.
(Other definitions for spot that I've seen before include "Notice - place" , "Notice; sign of acne" , "Dot, stain" , "Notice; mark" , "Small mark; see" .)