The Athletics outrighted Barrera to Triple-A Las Vegas on Sunday.
Oakland has now moved Barrera off its 40-man roster on two occasions this season, with the 26-year-old outfielder clearing waivers both times. Barrera has seen action in 32 games with the Athletics this season, but he's spent the bulk of the campaign in Las Vegas, where he's produced a .271/.331/.451 batting line over 294 plate appearances.