Part of leg in young animal (4)
I believe the answer is:
calf
This clue is a double definition.
'part of leg' is the first definition.
('calf' is part of 'leg')
'young animal' is the second definition.
(I've seen this before)
'in' is the link.
(Other definitions for calf that I've seen before include "Young animal associated with soft leather" , "Young moo-er" , "Young animal; part of body" , "stocking filler" , "Young cow or bull" .)