Johnson arrived in St. Petersburg on Monday night and flew right back out very early Tuesday morning, O's manager Dave Trembley said. There's no timetable for Johnson's return.
Danys Baez will assume the closing duties with Johnson away.
"We can't fill his roster spot," Trembley said. "There's no list you can put him on. I don't know when he'll be back."
The Orioles promoted reliever Kam Mickolio from Triple-A Norfolk on Monday night to replace struggling right-hander Matt Albers, who was optioned down, and Trembley said he feels the relief corps is in slightly better shape than it had been. But losing Johnson for any length of time is a blow to a unit already stretched thin.
"It's better than it was last night," Trembley said. "Last night was next to bare bones. Tonight there's some meat on the hook."
The Orioles had to use three relievers in Monday night's 8-5 loss to the Angels after starter David Hernandez went 5 1/3 innings. That came after Sunday's 13-inning loss in which the relief corps had to throw 7 1/3 frames.
Baez, who hasn't pitched since Sunday, is 4-6 with a 4.18 ERA in 42 games this season. He has yet to record a save.
Zach Schonbrun is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.