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Las Vegas NEEDS Conor McGregor ... Conor McGregor does NOT NEED Las Vegas ... so says Dana White.

The UFC boss says the Nevada State Athletic Commission made a TREMENDOUS mistake in fining Conor $150k for his water bottle incident because it'll cost THEM a lot more in the end.

"If you threw a water bottle and got fined $150,0000 would you fight there again?"

"[Conor] can fight in Iowa and sell tickets. He can fight on an island off the coast of Peru and sell tickets," White said.

"Las Vegas needs him. He doesn't need Las Vegas."

There's more ... White also talked about the return of Ronda Rousey as he left Mr Chow in Bev Hills Wednesday night and explained why she's still a force to be reckoned with.