The most common and most likely answer to this crossword clue is the 9 letter word INSOMNIAC
I've seen this crossword clue in The Guardian
I
N
S
O
M
N
I
A
C
More clues leading to the result INSOMNIAC
- One can't go off at nights
- Wakeful type in county recalled famous murderer
- One manic son unfortunately is not sleeping
- I often can’t go out when I want
- One often up probably wasting money in casino
- Simon’s gone crazy and turned killer and he can’t sleep at night
- Current issue involves money — first clue one probably won’t enjoy retirement
- One taken in by awful conman is suffering from sleep deficit
- One that’s unable to be out?
- One maybe needing number and coins, frantically, to ring Mina abroad
Buddy explains!

The straight part
We know that "one probably won’t enjoy retirement" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case one probably won’t enjoy retirement = insomniac.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 INSOMNIAC mean?
INSOMNIAC noun- One who suffers an inability or difficulty sleeping; a sufferer from insomnia.
- Suffering from or pertaining to insomnia.