The most common and most likely answer to this crossword clue is the 7 letter word NO-GOOD
I've seen this crossword clue in The Guardian
N
O
-
G
O
O
D
More clues leading to the result NO-GOOD
Buddy explains!

The straight part
We know that "Worthless" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case worthless = no-good.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 NO-GOOD mean?
NO-GOOD noun- A worthless or useless person
- Having no value, use or merit