The Athletics designated Diaz for assignment Tuesday.
Diaz has gone just 3-for-29 in 12 games with the A's this season, and his poor performance has now officially caused him to lose his 40-man roster spot. The 33-year-old owns just a .621 OPS over 32 plate appearances in the minors this season, making it likely he passes through waivers unclaimed. Brett Harris was recalled from Triple-A Las Vegas in a corresponding move.