The most common and most likely answer to this crossword clue is the 2 plus 2 plus 3 plus 4 plus 3 letter word IN AT THE DEEP END
I've seen this crossword clue in Financial Times
I
N
A
T
T
H
E
D
E
E
P
E
N
D
More clues leading to the result IN AT THE DEEP END
Buddy explains!
The straight part
We know that "Very much out of one’s comfort zone" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case very much out of one’s comfort zone = in at the deep end.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.