Atkins, who made seven relief appearances the last two seasons for the Chicago Cubs, will take the mound Tuesday night at Texas.
The Orioles cleared a roster spot by putting outfielder Luke Scott on the 15-day disabled list. Scott, hitting .223 with nine home runs, has been playing through a right labrum tear. He last played Sunday.
"It wasn't doing him any good or us any good for him to try to play through it," manager Buck Showalter said. "We all know what Luke's capable of doing when he's right. You know how frustrated he gets, and I'm frustrated for him more than anything. It's not for a lack of trying or doing everything possible off the field possible to get back."
Showalter said Scott would have an examination where dye is injected into the injured area.
"We'll get a better feel if there are any changes," Showalter said. "Then we'll take advantage of the All-Star break. I think he's gonna be fine."
The Orioles are hopeful that Scott can be back by the time they play their second series after the All-Star break.
Baltimore needed a starting pitcher after Alfredo Simon, who had been a candidate to pitch the middle game of the series, was instead needed to pitch 4 1/3 innings in relief Monday night. Baltimore starter Chris Jakubauskas gave up six runs while facing only 13 batters in a 13-4 loss to the Rangers.