Krook was returned to Triple-A Scranton/Wikes-Barre after Saturday's doubleheader against the Cardinals.
Krook was called up to provide depth to the Yankees' bullpen, and he worked 1.1 innings in the opening game of the doubleheader. That outing was his second appearance in the majors, and he could return to work low-leverage relief innings in the second half of the campaign.