"It would be my normal bullpen day so I'm probably going to throw my bullpen [Sunday]," Guthrie said. "That would put me on pace to start Tuesday or Wednesday this week, depending on what works best for the rotation.
"There are a lot of X-factors with doubleheaders and everything else. I'd say that Tuesday and Wednesday are the most likely days."
The uncertainty around Guthrie, who was originally Saturday's starter but was pushed back due to the soreness, is also keeping the rest of the Orioles rotation in flux. Beyond Brian Matusz and Zach Britton, who will throw Sunday and Monday, respectively, the rotation for the rest of the week is still up in the air.
"We will take it a step at a time," Orioles manager Buck Showalter said of Guthrie's situation. "He's had a lot of work trying to get a feel for it. Until he actually gets a ball in his hand, we won't really know."
Right-hander Alfredo Simon was available for emergency use in the bullpen Saturday, although Showalter said he will try to stay away from using him because Simon -- right now -- is still part of the rotation.
Brittany Ghiroli is a reporter for MLB.com. Read her blog, Britt's Bird Watch, and follow her on Twitter @britt_ghiroli. This story was not subject to the approval of Major League Baseball or its clubs.