"It just tightened up on me over the off-day [Thursday]," O'Flaherty said. "It's something I've dealt with before in the past. We just kind of take it day by day. It usually clears itself up in two or three days."
O'Flaherty played catch on Sunday and will throw a bullpen session in Chicago on Monday when the A's open a series against the White Sox. He said his back feels better than it did when the Astros series began, so he expects to be available soon.
In 15 games since Doolittle was sidelined, the A's have had just two save situations.
Aaron Leibowitz is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.