Everyone who thinks Justin Bieber's soccer skills are legit have been living a damn lie ... because former USA coach Bruce Arena says the Biebs just ain't got it.
We got Arena out at LAX and wanted to know what an expert (even though we missed the World Cup, he's an expert) thought about Bieber's prowess on the pitch.
Our guy showed Arena some video -- then asked if he thought Biebs was any good at soccer. Unfortunately for Justin, the old coach kept it 100%, A-1, 24 carat real.
"I don't think that. I think he's better off doing what he's doing."
Don't be mad at us Justin ... we tried to remind Bruce that you're friends with Neymar and asked if you could maybe make the MLS if Neymar helped -- but Arena had a simple answer to that too.
It's not too late to say you're sorry Bruce ... TO ALL AMERICANS FOR MISSING THE FREAKIN' WORLD CUP!