The most common and most likely answer to this crossword clue is the 9 letter word INCAPABLE
I've seen this crossword clue in The Times
I
N
C
A
P
A
B
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E
More clues leading to the result INCAPABLE
- Helpless where demented pelican ingests tar
- Leap in cab awkwardly, helplessly drunk
- Incompetent at home, father gets entangled in flex
- Useless rain-cap a blemish exposed
- Drunk Peruvian artist dismissed from lesson?
- Old South American allegory — rejecting god is useless
- Some win cap — a bleary-eyed drunk!
- Smart guy holding old man powerless
- Elected, a political leader into message that’s hopeless
- One new guy embracing secretary is impotent
Buddy explains!
The straight part
We know that "Not up to it" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case not up to it = incapable.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does INCAPABLE mean?
INCAPABLE noun- One who is morally or mentally weak or inefficient; an imbecile; a simpleton.
- Not capable (of doing something); unable.
- Not in a state to receive; not receptive; not susceptible; not able to admit.