The most common and most likely answer to this crossword clue is the 2 plus 3 plus 7 letter word IN THE BALANCE
I've seen this crossword clue in Financial Times
I
N
T
H
E
B
A
L
A
N
C
E
Buddy explains!
The straight part
We know that "At a critical stage" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case at a critical stage = in the balance.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.