A difficult problem (1,4,3,2,5)
I believe the answer is:
a hard nut to crack
'a difficult problem' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for a hard nut to crack that I've seen before include "formidable opponent" , "It takes a lot of sorting out" , "formidable opposition" , "Brazil could be" , "Brazil creating problem" .)