Lose one's shirt, ultimately bearing torso and chest (2,4)
I believe the answer is:
go bust
'lose one's shirt' is the definition.
(I've seen this in another clue)
'ultimately bearing torso and chest' is the wordplay.
'ultimately' suggests the final letters.
'and' is a charade indicator (letters next to each other).
'chest' becomes 'bust' (bust can mean a woman's chest).
The last letters of 'bearing torso' are 'go'.
'go'+'bust'='GO BUST'
(Other definitions for go bust that I've seen before include "Not get out of the red" , "so firm might collapse" , "Become bankrupt" .)