In a precarious position (3,2,1,4)
I think it could be either:
out on a limb
(Other definitions for on thin ice that I've seen before include "that can make one vulnerable" , "sailing close to the wind?" , "In a precarious situation" , "in danger of a soaking?" , "At risk" .)
'in a precarious position' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for out on a limb that I've seen before include "Exposed, vulnerable" , "In a precarious position" , "In a vulnerable position" , "questionably placed" , "Alone and in danger" .)