The Reds moved Zimmer to minor-league camp Tuesday.
Zimmer was one of four Reds pitchers removed from big-league camp in the organization's latest round of roster cuts in advance of Opening Day. The 30-year-old right-hander had made 83 appearances for the Royals over the past three seasons, producing a 5.19 ERA, 1.54 WHIP and 7.5 K-BB% across 95.1 innings. He'll likely begin the season as a member of the bullpen at Triple-A Louisville.