The most common and most likely answer to this crossword clue is the 9 letter word DOG-TIRED
I've seen this crossword clue in The Times
D
O
G
-
T
I
R
E
D
Buddy explains!
The straight part
We know that "Worn-out" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case worn-out = dog-tired.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 DOG-TIRED mean?
DOG-TIRED adjective- Exhausted