Left-handed reliever Brian Matusz is out indefinitely with a lower back injury he suffered during his first spring training appearance Wednesday.
Matusz underwent an MRI on his lower back Thursday, but Showalter said that he didn't expect Matusz to make his next scheduled spring appearance.
"They've talked to me about it, what they think, but let's kind of get there first," Showalter said. "His return is not imminent. … [Let's] see how he feels tomorrow and see where we are with it. We got the information back and doc's going to look at it when [they] gets back."
Matusz pitched the fifth inning in the Orioles' 11-4 Grapefruit League loss to the Atlanta Braves on Wednesday, allowing two hits, including a solo homer to Mallex Smith.
"He just felt it during the game," Showalter said. "It was pretty sore, kind of in the lower back, on the side, the way I understand it. He initially requested the MRI, and [the team] thought it would be a good idea. We just want to know what we're dealing with here. He said it's just been kind of sore. Yesterday was a little bit more than that."
Matusz has never missed time with a back injury over the course of his career. He had surgery on his nonthrowing shoulder this past offseason and also had surgery to repair a muscle in his abdomen during the offseason following the 2012 season.
Showalter wouldn't go as far as to say that the injury would be a disabled list situation had it been during the regular season.
"It's something that we've got to get our arms around," Showalter said. "I don't think we're there yet. Next couple days, see how he responds. But he's not going to be back in there on his normal turn. It's kind of strange. I'm really anxious to hear the dynamic of how it all came about."
Matusz, who was 1-4 with a 2.94 ERA last season serving as the Orioles' left-handed specialist, held left-handed hitters to a .186 batting average in 2015.
Right-hander Yovani Gallardo is scheduled to face hitters for the first time Saturday. He will then make his first spring start in the middle of next week. … Right-hander Chris Tillman, who has been slowed by tightness in his hip flexor, is schedule to throw a bullpen session Friday. He could also make his Grapefruit League debut in the middle of next week. … Right-hander Tyler Wilson will start Saturday's day split-squad game against the Minnesota Twins in Fort Myers and right-hander Kevin Gausman will start the home night game against the Rays at Ed Smith Stadium. ... When minor league infielder Corban Joseph, the younger brother of Orioles catcher Caleb Joseph, entered Thursday's game as a pinch hitter in the ninth inning, it marked the first time the Joseph brothers played in the same game for the same team since Caleb's senior year of high school at Franklin (Tenn.). They didn't play at the same time — Caleb started and exited the game in the bottom of the sixth — but it still marked a big day for the brothers, who haven't played together since 2008.