The move was retroactive to Saturday.
The first baseman, who left Friday night's game against Kansas City after four innings, had earlier expressed confidence that he would soon return from the injury. However, after receiving an MRI on Saturday, the results indicated that rest would be the best course of action.
"A little bit worse than what we thought it was going to be," Davis said Saturday night. "It's kind of crazy because I don't feel terrible. I've never had anything like this before. I figured it would just be a few days and then we'd forget about it."
Baltimore did not make a move Sunday to fill the roster spot. The Orioles are off Monday, and manager Buck Showalter said the team will fill out the 25-man roster before Tuesday's game against Pittsburgh.
Davis led the majors last season with 53 home runs and 138 RBIs. He has only two homers and 13 RBIs this season, and it will be a while before he gets to add to that total.
"I guess the DL is the best choice right now," he said. "Hopefully things will go well and I'll be able to bounce back quickly."
Earlier in the day, Davis expressed confidence that he wouldn't miss more than a few games.
"It's definitely disappointing, frustrating," he said. "I do a lot to try and take care of my body and prevent injuries. You play this game long enough eventually you're going to run into something like this. But I'm going to stay positive."
It is uncertain when the injury occurred, although Davis suspected the muscles in his left side might have been weakened when he dived for groundballs in Boston and Toronto before the Orioles returned home to face the Royals.
On Friday night, Davis winced after hitting a flyball in the third inning. He played another inning before Showalter removed him from the game.
Now, it appears as if Showalter will have to adjust to being without Davis for at least the next two weeks.
"It's something we think will take the DL period at a minimum, so we'll start with that (Sunday)," the manager said.
Right fielder Nick Markakis was in the starting lineup at first base Saturday night. Before batting practice, three Baltimore coaches worked with Markakis at the position, going over throws and positioning.
Utility infielder Ryan Flaherty also is expected to get time at first base. Flaherty has been playing third base while the Orioles wait for Manny Machado to come off the disabled list following offseason knee surgery.
Asked if subbing for Davis, an All-Star last season, will be imposing, Flaherty replied, "I got stuck trying to do that for Manny the first couple weeks."
Machado could play in Class A Frederick or Norfolk on Monday. It appears the Minnesota series on May 2-4 could be the most likely time for him to return to the Orioles, Showalter confirmed.
The Associated Press contributed to this report.