The most common and most likely answer to this crossword clue is the 5 letter word POILU
I've seen this crossword clue in The Guardian
P
O
I
L
U
More clues leading to the result POILU
Buddy explains!

The straight part
We know that "soldier abroad" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case soldier abroad = poilu.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 POILU mean?
POILU noun- A French infantryman during the First World War