Slim, not up to it, depended upon others (5,2)
I believe the answer is:
leant on
'depended upon others' is the definition.
I can't judge whether this defines the answer.
'slim not up to it' is the wordplay.
'slim' becomes 'lean' (similar in meaning).
'up' is a reversal indicator (in down clue: letters go upwards).
'to it' is a charade indicator (letters next to each other).
'not' reversed gives 'ton'.
'lean'+'ton'='LEANT ON'
Can you help me to learn more?
(Other definitions for leant on that I've seen before include "Depended upon" , "Pressed" .)