The Athletics recalled Barnett from Triple-A Las Vegas on Tuesday.
Barnett made one scoreless relief appearance for the Athletics earlier this season but has spent most of the year in the rotation at Las Vegas, holding a 4.64 ERA and 41:26 K:BB over 42.2 innings. He could get a chance to make some starts for the Athletics, though the club has not yet clarified what Barnett's role will be.