The most common and most likely answer to this crossword clue is the 11 letter word SCRATCHCARD
I've seen this crossword clue in The Sunday Telegraph
S
C
R
A
T
C
H
C
A
R
D
Buddy explains!

The straight part
We know that "probable loser" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case probable loser = scratchcard.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 SCRATCHCARD mean?
SCRATCHCARD noun- A lottery ticket containing sections covered with an opaque waxy film which may be removed by scratching to reveal symbols that show whether or not a prize has been won