Expert is left gambling on dollar with no gain (10)

I believe the answer is:

profitless

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

'expert' is the definition.
Both the definition and answer are adjectives. Maybe you can see an association between them that I can't see?

'left gambling on dollar with no gain' is the wordplay.
I cannot really understand how this works, but
'left' could be 'l' (common abbreviation) and 'l' is located in the answer.
'dollar' could be 's' and 's' is located in the answer.
'no' could be 'o' (resembles 0 - 'no' can mean 'zero') and 'o' is located in the answer.
This explanation may well be incorrect...

'is' is the link.

Can you help me to learn more?

I've seen this clue in The Guardian.

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