Kranick was optioned to Triple-A Indianapolis on Monday, Jason Mackey of the Pittsburgh Post-Gazette reports.
Kranick tossed five perfect innings in his major-league debut against the Cardinals on Sunday, and general manager Ben Cherington revealed Sunday that the team plans to proceed with a six-man rotation through at least the All-Star break. While the right-hander is a strong candidate to make another start in the near future, he'll head back to the minors after right-hander Cody Ponce was recalled from Triple-A Indianapolis.