The most common and most likely answer to this crossword clue is the 7 letter word EARTHEN
I've seen this crossword clue in The Daily Telegraph
E
A
R
T
H
E
N
More clues leading to the result EARTHEN
- Lug in that case of clay
- Deserve to retain article made of clay
- Are rocks, therefore, like pottery?
- Small figure missing from coin made of clay
- A tree mostly cultivated on a layer of clay
- Hint of residue found on each model bird made of clay
- Made of clay, shell-like article held up by knight
- Many a crock is needing attention in that case
- Deservedly get to hold article of baked clay
- Eastern sculpture, perhaps, bird in clay
Buddy explains!

The straight part
We know that "Made of clay" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case made of clay = earthen.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 EARTHEN mean?
EARTHEN adjective- Made of earth or mud.
- Made of clay (especially said of pottery).
- Earthly.
- To provide or add soil to
- To make earthly or earthlike