Holmes was assigned to Triple-A Indianapolis on Monday, Rob Biertempfel of the Pittsburgh Tribune-Review reports.
Though the Pirates added Holmes to the 40-man roster during the offseason, the right-hander wasn't in serious consideration for an Opening Day role with the big club. He'll still move up a rung in the ladder to Triple-A after logging a 4.22 ERA, 1.48 WHIP and 101 strikeouts over 136.1 innings at Double-A Altoona in 2016.