The most common and most likely answer to this crossword clue is the 7 letter word ANXIOUS
I've seen this crossword clue in The Sunday Telegraph
A
N
X
I
O
U
S
Buddy explains!

The straight part
We know that "Concerned" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case concerned = anxious.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 ANXIOUS mean?
ANXIOUS adjective- Nervous and worried.
- Having a feeling of anxiety or disquietude; extremely concerned, especially about something that will happen in the future or that is unknown.
- (of things) Accompanied with, or causing, anxiety; worrying.
- Earnestly desirous.