Game involving some loss of blood? (3)

I believe the answer is:

loo

I'm a little stuck... Click here to teach me more about this clue!

'game' is the definition.
(historical card game)

'some loss of blood?' is the wordplay.
'LOO' is hidden within the letters.
However, I am unsure how this is indicated.

'involving' is the link.

Can you help me to learn more?

(Other definitions for loo that I've seen before include "Ladies, perhaps" , "Little boys' room" , "In which one goes" , "Card-game" , "Privy" .)

I've seen this clue in the Evening Standard.

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