The most common and most likely answer to this crossword clue is the 4 plus 2 plus 4 letter word FEET OF CLAY
I've seen this crossword clue in Financial Times
F
E
E
T
O
F
C
L
A
Y
More clues leading to the result FEET OF CLAY
- Unexpected weaknesses that held boxer up?
- Hidden weakness of boxer’s supporters
- Weakness? No, these used to float like a butterfly
- Character flaws revealed by wager after payment to soccer team
- Those that supported Cassius show unsuspected faults
- Weaknesses shown by supporters of Cassius?
- Extremities associated with once the greatest fundamental weakness?
- Supports for “floater” and “stinger|” showing unexpected weakness
- Hidden flaw in some poetry from Muhammad Ali?
Buddy explains!

The straight part
We know that "Weakness" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case weakness = feet of clay.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.