Diplan was optioned to Triple-A Norfolk on Sunday, Roch Kubatko of MASNSports.com reports.
Diplan spent just under two weeks in the Orioles' bullpen, and he allowed a run on two hits and five walks while striking out eight in 5.1 innings over four appearances during his time with the major-league club. However, he hadn't pitched since May 31 and should see more consistent work in the minors.