The most common and most likely answer to this crossword clue is the 11 letter word HAEMOPHILIA
I've seen this crossword clue in The Times
H
A
E
M
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P
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A
Buddy explains!
The straight part
We know that "blood problem" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case blood problem = haemophilia.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 HAEMOPHILIA mean?
HAEMOPHILIA noun- Any of several hereditary illnesses that impair the body's ability to control bleeding, usually passed from mother to son.