The most common and most likely answer to this crossword clue is the 9 letter word SLIMEBALL
I've seen this crossword clue in The Times
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More clues leading to the result SLIMEBALL
Buddy explains!

The straight part
We know that "creep" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case creep = slimeball.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 SLIMEBALL mean?
SLIMEBALL noun- A round lump made up of or coated with slime or a slime-like substance such as mucus.
- (originally United States) A person who is regarded as slimy (that is, sneaky or underhanded) or otherwise undesirable.