The Athletics optioned Barnett to Triple-A Las Vegas on Tuesday.
The transaction comes one day after Barnett was lit up for six runs over 2.2 innings in a loss to the Royals. With Jeffrey Springs (hip) slated to rejoin the Athletics' rotation this week, Barnett will lose his spot among the starting five and has now logged a 7.08 ERA, 1.62 WHIP and 38:24 K:BB over 40.2 frames in 2026.