Could that return come as early as Sept. 9 or 10, which Showalter mentioned previously?
"Probably not," Showalter said.
Still, the O's are cautiously optimistic the righty -- who has been the club's best starter -- can return by mid-month.
Tillman is 15-5 with a 3.76 ERA in 26 starts, and he last pitched in a game on Aug. 20.
Brittany Ghiroli has covered the Orioles for MLB.com since 2010. Read her blog, Britt's Bird Watch, follow her on Facebook and Twitter @britt_ghiroli, and listen to her podcast. This story was not subject to the approval of Major League Baseball or its clubs.