Castillo will pitch following opener Carlos Hernandez against the White Sox on Sunday, Pete Grathoff of The Kansas City Star reports.
Castillo will get a chance to work multiple innings following Hernandez on Sunday against Chicago. In three appearances thus far with the Royals, Castillo has registered a 2.89 ERA over 9.1 innings, but he has walked six while accumulating a 1.50 WHIP.