Conor McGregor was an awesome rags to riches story ... before he went nuts and attacked a damn bus -- so says UFC star Justin Gaethje.
We spoke with Justin -- one of the top fighters in McGregor's 155-pound division -- and he told us Conor's an extreme example of broke fighters who get too much, too soon.
"McGregor wasn’t rich 5 years ago. Now, you put $100 million in his pocket and you see how it changes people," Gaethje told TMZ Sports.