The most common and most likely answer to this crossword clue is the 5 plus 5 letter word KNOCK KNEED
I've seen this crossword clue in Financial Times
K
N
O
C
K
K
N
E
E
D
Buddy explains!

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.
Crossword Answer definitions
KNOCK KNEED adjective- (of the legs) having the knees abnormally close together, and the ankles spread apart
- (of a person or animal) suffering from genu valgum (or tibia valga)