The most common and most likely answer to this crossword clue is the 11 letter word INOPPORTUNE
I
N
O
P
P
O
R
T
U
N
E
Buddy explains!

The straight part
We know that "unsuitable’" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case unsuitable’ = inopportune.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.
Crossword Answer definitions
INOPPORTUNE adjective- Unsuitable for some particular purpose
- At an inconvenient or inappropriate time