The most common and most likely answer to this crossword clue is the 7 letter word EDGIEST
I've seen this crossword clue in Financial Times
E
D
G
I
E
S
T
More clues leading to the result EDGIEST
Buddy explains!

The straight part
We know that "Most nervous" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case most nervous = edgiest.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 EDGIEST mean?
EDGIEST adjective- Nervous, apprehensive.
- (entertainment) Creatively challenging; cutting edge; leading edge.
- (entertainment) On the edge between acceptable and offensive; pushing the boundaries of good taste; risqué.
- Irritable.
- Having some of the forms, such as drapery or the like, too sharply defined.
- (of a knife or blade) Sharp.
- Cool by virtue of being tough, dark, or badass.
- Exhibiting behavior that is disconcerting or alarming, sometimes in an effort to impress or to troll others.