The move was made official pregame on Saturday.
Interim manager Juan Samuel confirmed Montanez has not been available since Wednesday with a left oblique injury suffered during pregame batting practice.
"This has been the worst year of my career," said Montanez, who was batting .140 in just 57 Major League at-bats. "It's like everything has gone completely backwards. The hits haven't fallen, the at-bats haven't been there, now I get injured."
It hasn't been all roses for Atkins either. Playing first base on Friday in lieu of Ty Wigginton, who was dealing with back tightness, Atkins made just his fifth start in 22 games.
Prior to Samuel's announcement, Atkins said he was confident he would be around for the next few days, but beyond that, his future is clouded. The soft-spoken Atkins, who has remained professional in the wake of being delegated to the bench, isn't immune to the rumors that have been swirling concerning the Orioles releasing him.
"They might have given up on me, but I don't think [my release] is going to happen this weekend," Atkins said. "I don't think I'd be playing [on Friday] if the plan is to get rid of me after the game."
Atkins entered the series opener against the Nationals batting .219 with just one homer and nine RBIs. Tuesday's trade for right-handed bat Jake Fox all but guaranteed Atkins' tenure in Baltimore was coming to an end.
"I know [Samuel] feels bad, there's only so many spots to go around in the lineup," said Atkins, who is 8-for-55 in his past 20 games. "Guys that have been in my position have done a good job. So you can't really complain about not playing when guys are playing good."
Atkins will likely remain with the team until injured outfielder Felix Pie comes back. Pie started a rehab assignment with Class A Advanced Frederick on Thursday and could be activated when the Orioles' homestand ends on July 2.
With his time nearing an end in Baltimore, Atkins acknowledged that it could be a blessing in disguise. Recently released Rays designated hitter Pat Burrell has found a new home and regained his power stroke in San Francisco, and Atkins said when the O's cut ties, he won't look at it as a bad thing.
"Not at all," he said. "[It would] be a welcome opportunity."
Atkins was non-tendered by the Colorado Rockies after the 2009 season and was signed by the Orioles to a one-year contract guaranteed to net him $4.5 million this season. Baltimore has a club option for 2011.
Brittany Ghiroli is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.