One facing problem, weighed down by work (7)
I believe the answer is:
opposer
'one facing' is the definition.
The definition suggests a singular noun which matches the answer.
'problem weighed down by work' is the wordplay.
'problem' becomes 'poser' (poser is a kind of problem).
'weighed down by' means one lot of letters go next to another (in a down clue, some letters go on top of others).
'work' becomes 'op' (short for opus).
'poser' put after 'op' is 'OPPOSER'.
Can you help me to learn more?
(Other definitions for opposer that I've seen before include "Propose to challenger" , "Second to speak" , "The one against the motion" , "Second speaker in debate" , "One resisting" .)