Strop said he was worried and has been thinking about his back for a little while, but he doesn't want to blame his early season struggles on the injury. The 27-year-old has a 6.11 ERA and has walked 14 batters over 17 2/3 innings of work.
"Sometimes you have something going on in your body that's not right," said Strop, who allowed two runs and issued a pair of walks on Thursday against Toronto. "I was just thinking about myself and my career, and what is the best for me in this moment, this time. It finally got to the point where I thought, 'OK, this has got to be fixed.'"
The Dominican Republic native, who hopes to be activated right when eligible, said this was the right move to make instead of fighting through the pain and potentially being forced to sit out longer later in the season.
Showalter said Strop's back pain is an issue that has been lingering too long for the club's liking.
"Trying to get it completely taken care out," Showalter said. "It might even be good for him in the long run, too."
Johnson, meanwhile, was called on immediately, logging 2 2/3 innings in Baltimore's 6-5 win over the Blue Jays on Saturday. Despite allowing a pair of runs in the eighth, Showalter was pleased with Johnson's effort. The right-hander punched out five batters in his first relief appearance of the season.
"That was big to get him in here," Showalter said. "I had three [relievers] I was not going to pitch today."
Despite starting at Norfolk, where he went 1-2 with a 5.49 ERA, Johnson will work exclusively as a reliever while he's up with the Orioles. The 25-year-old logged 38 1/2 innings in 2012, his first season in the Majors, making eight relief appearances.
Chris Toman is a contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.