"We talked, and after two or three days if it wasn't getting better, there might be something in there that caused him to not get better," manager Buck Showalter said of Thome, who left the team on Monday to travel back to Baltimore. "Especially with some of the treatment, we've seen a lot of these things mange itself in a day or so. So I wasn't surprised [with the news] today."
Infielder Robert Andino was activated from the DL to take Thome's place, and the plan is for the veteran designated hitter to go to California for an epidural from a doctor he's more familiar with from previous injuries.
Thome said he first felt some discomfort when he woke up on Saturday morning. He was put on anti-inflammatory medication and had trigger-release treatment earlier in the week but wasn't making the progress that the team had hoped for, which is why he underwent the MRI exam on Tuesday.
Acquired from the Phillies in a July 1 trade, Thome has hit .261 with two homers and six RBIs in 18 games with the Orioles. Chris Davis has served as the O's primary DH in Thome's place, and Showalter wasn't willing to speculate if Thome could be out longer than the 15-day period.
"Hopefully he can get that injection in the next couple days and make it back on the 12th [of August]," Showalter said.
Andino is coming off the DL, having been sidelined with a left shoulder strain. He played for Triple-A Norfolk the previous two days with no pain, going 3-for-9 with two RBIs, a walk, a run scored and an error.
"I swung really hard and let my bat go, and there's no pain," Andino said of his shoulder. "I got scared for a minute, but there's no pain."
The O's Opening Day second baseman, Andino hit .230 with five homers and 21 RBIs in 79 games before landing on the DL. In his absence, the Orioles traded for infielder Omar Quintanilla and have used him primarily at second base. Quintanilla, who entered Tuesday hitting .429 with a homer and three RBIs, got the start again on Tuesday and hit a two-run single during Baltimore's seven-run top of the second.
"We will use both their skills and where they are and what the matchups are," Showalter said of his plans for the pair of infielders. "We feel really good to have two versatile players like Robert and Q. So we will see the way it takes itself and take advantage of a given part of the season. If someone is swinging the bat well and doing certain things, we will ride it."
Brittany Ghiroli is a reporter for MLB.com. Read her blog, Britt's Bird Watch, and follow her on Twitter @britt_ghiroli. This story was not subject to the approval of Major League Baseball or its clubs.