The most common and most likely answer to this crossword clue is the 9 letter word PALTRIEST
I've seen this crossword clue in The Daily Telegraph
P
A
L
T
R
I
E
S
T
More clues leading to the result PALTRIEST
Buddy explains!

The straight part
We know that "Most worthless" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case most worthless = paltriest.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 PALTRIEST mean?
PALTRIEST adjective- Trashy, trivial, of little value.
- Of little monetary worth.