The Yankees recalled Krook from Triple-A Scranton/Wilkes-Barre on Saturday.
Krook is a 28-year-old southpaw who has yet to make his big-league debut. He converted to relief with Scranton/Wilkes-Barre this season with promising results, recording a 1.04 ERA and 47.9 percent strikeout rate in 17.1 innings, though he also walked 16.9 percent of the batters he faced. He'll presumably start out in a low-leverage role until he proves he can have similar success against MLB bats.