The most common and most likely answer to this crossword clue is the 10 letter word UNDERGOING
I've seen this crossword clue in The Daily Telegraph
U
N
D
E
R
G
O
I
N
G
More clues leading to the result UNDERGOING
Buddy explains!

The straight part
We know that "suffering" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case suffering = undergoing.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 UNDERGOING mean?
UNDERGOING verb- To go or move under or beneath.
- To experience; to pass through a phase.
- To suffer or endure; bear with.