The most common and most likely answer to this crossword clue is the 8 letter word RELAPSED
I've seen this crossword clue in The Daily Telegraph
R
E
L
A
P
S
E
D
More clues leading to the result RELAPSED
- Legs covered in grass got worse
- Within plant, circuits failed again
- Oddly pleased after end of pier fell away
- Dropped back and fell asleep in road
- Slip into debt, having fallen ill once more
- Suffered setback regarding drink and speed regularly taken
- English king upset large part of church before start of divorce is declined
- Embarrassed about mistake, failed
- Wine drinking wrong, it has gotten worse
Buddy explains!

The straight part
We know that "Suffered setback" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case suffered setback = relapsed.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 RELAPSED mean?
RELAPSED verb- To fall back again; to slide or turn back into a former state or practice.
- (of a disease) To recur; to worsen, be aggravated (after a period of improvement).
- To slip or slide back physically; to turn back.