Hearn was optioned to Triple-A Round Rock following Saturday's victory over the Nationals.
Hearn will report to Round Rock after he was recently moved to the Rangers' bullpen. The left-hander has struggled greatly this season, posting a 6.25 ERA and 1.75 WHIP with 54 strikeouts over 59 innings in 13 starts. It remains unclear who will replace Hearn in the starting rotation, but the team is expected to make a corresponding move Sunday.