Masterson's next step will be a bullpen session off a mound on Friday in Cleveland.
"That's really exciting," manager Terry Francona said. "Just the fact that he's feeling better so fast is good for everybody's peace of mind. And the fact that he might be able to come back and pitch, and help us win, is even better."
Due to the fact that Cleveland only has 11 games (including Wednesday's tilt against the Royals) left in the regular season, it is unclear whether Masterson would return as a starter or reliever, if he can indeed be ready prior to the postseason.
Entering Wednesday, the Indians sat a half-game back of both the Rays and Rangers for one of the American League's Wild Card spots.
In 29 starts this season, the 28-year-old Masterson is 14-10 with a 3.52 ERA and 188 strikeouts in 189 1/3 innings. The sinkerballer went 4-2 with a 2.87 ERA in the nine outings leading to his outing against Baltimore on Sept. 2, when he exited with the injury after facing only five batters.
Masterson, who was diagnosed with a strained left oblique after underoing an MRI, resumed a throwing program last Thursday in Chicago. The Tribe's ace has been extremely encouraged by how he has bounced back from the injury.
"Prayers have been answered," Masterson said with a smile.
Jordan Bastian is a reporter for MLB.com. Read his blog, Major League Bastian, and follow him on Twitter @MLBastian. This story was not subject to the approval of Major League Baseball or its clubs.