Bone up a little, covering Italy (5)
I believe the answer is:
tibia
'bone' is the definition.
(tibia is a kind of bone)
'up a little covering italy' is the wordplay.
'up' says the letters should be written in reverse (in down clue: letters go upwards).
'a little' becomes 'abit' ('a bit' can be a synonym of 'a little'**).
'covering' is an insertion indicator.
'italy' becomes 'i'.
'abit' placed around 'i' is 'aibit'.
'aibit' reversed gives 'TIBIA'.
(Other definitions for tibia that I've seen before include "Part of leg of" , "The formal shinbone" , "The large shinbone" , "Bone in osso bucco" , "part of skeleton" .)