The most common and most likely answer to this crossword clue is the 7 letter word WHACKED
I've seen this crossword clue in The Guardian
W
H
A
C
K
E
D
Buddy explains!
The straight part
We know that "Dog-tired" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case dog-tired = whacked.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 WHACKED mean?
WHACKED verb- To hit, slap or strike.
- To kill, bump off.
- To share or parcel out; often with up.
- To beat convincingly; to thrash.
- (usually in the negative) To surpass; to better.
- Tired; fatigued.
- Intoxicated on drugs.