The most common and most likely answer to this crossword clue is the 10 letter word DISPARAGED
I've seen this crossword clue in The Sunday Telegraph
D
I
S
P
A
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A
G
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D
More clues leading to the result DISPARAGED
Buddy explains!

The straight part
We know that "denigrated" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case denigrated = disparaged.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 DISPARAGED mean?
DISPARAGED verb- To match unequally; to degrade or dishonor.
- To dishonor by a comparison with what is inferior; to lower in rank or estimation by actions or words; to speak slightingly of; to depreciate; to undervalue.
- To ridicule, mock, discredit.