Speier was optioned to Triple-A Omaha on Wednesday, Lynn Worthy of The Kansas City Star reports.
Speier returned from the COVID-19 injured list last week and will now head back to the minors. The left-hander has a 2.33 ERA, 1.09 WHIP and 14:5 K:BB over 19.1 innings this season for the Royals, so it should only be a matter of time before he's back in the majors.