Setup man David Robertson also went for an MRI on Thursday, but his lower left hamstring strain will not require a DL stint, and the right-hander is day to day, Yankees general manager Brian Cashman said.
Cashman did not know who would be called up to replace Chamberlain, but said Triple-A righties Mark Montgomery, Preston Claiborne and Sam Demmel were under consideration.
Chamberlain's DL stint will be retroactive to April 28. Chamberlain, 27, last appeared in a game Saturday, picking up the save in the Yankees' 5-4 against the Toronto Blue Jays.
Chamberlain first felt the oblique pain warming up on Wednesday. Cashman said he thought the injury might only take two weeks to heal, but wasn't entirely certain.
"Joba is a pretty miraculous healer, more so than anyone else it seems," Cashman said. "He does get hurt, but when he does he usually bounces back pretty quick. At the very least, we are going to take the safe route."
Chamberlain has a 3.86 ERA in 9 1/3 innings this season, striking out seven and walking six.
A free agent after this season, Chamberlain talked this past spring about the possibility of becoming a starter again. But the Yankees view Chamberlain as a reliever, and he currently is serving as a seventh-inning man, leading into Robertson and Mariano Rivera.
The Yankees have nearly $100 million in salary on the disabled list but are 17-10. They start a series against the Oakland Athletics on Friday.