Diaz owns a .281 average and .836 OPS across 272 plate appearances over 66 games with Triple-A Las Vegas this season.
Diaz cleared waivers and was outrighted to Triple-A Las Vegas by the Athletics on Monday.
Diaz was designated for assignment by the Athletics on Thursday, Martin Gallegos of MLB.com reports.
Diaz was optioned to Triple-A Las Vegas on Sunday.
Diaz remains out of the lineup Friday versus the Angels.
Diaz is absent from the lineup for Thursday's contest in Minnesota.
Diaz is out of the lineup for Sunday's game versus the Tigers.
Diaz isn't in the Athletics' lineup Friday against Detroit.
Diaz isn't in the Athletics' lineup Tuesday against the Mariners.
Diaz went 2-for-5 with an RBI single and a double in a loss to the Rangers on Sunday.