Kilian was optioned to Triple-A Iowa on Tuesday, Maddie Lee of the Chicago Sun-Times reports.
The 25-year-old surrendered seven runs (five earned) over 2.1 innings Monday and will now make his way back to the minors. Kilian is Chicago's top pitching prospect, but he struggled across his first three starts in the majors with a 10.32 ERA, 2.03 WHIP and 9:12 K:BB in 11.1 innings.