Barreto was optioned to Triple-A Nashville on Tuesday.
Barreto will head back to the minors with Chad Pinder (elbow) back from the disabled list. The 22-year-old has shown power in his series of short stints with the Athletics this season, hitting four homers in 63 plate appearances, but his plate discipline is worrisome, as he's striking out 39.7 percent of the time and has walked just once.