Stadiums wherein Arsenal could ultimately lose money? (6)

I believe the answer is:

arenas

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

'stadiums' is the definition.
('arena' can be a synonym of 'stadium')

I can't explain the rest of the clue.

(Other definitions for arenas that I've seen before include "Structures for open-air sports or entertainments" , "Spaces in centre of stadiums" , "Areas for sports contests" , "Areas of endeavours" , "Sports venues" .)

I've seen this clue in the Evening Standard.

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