Walker (elbow, shoulder) is scheduled to throw a bullpen session Thursday, Nick Piecoro of the Arizona Republic reports.
If all goes well Thursday, the plan appears to be for Walker to open Sunday's season finale against the Padres with left-hander Alex Young coming in as the primary starter. Walker was expected to have a midseason return from Tommy John elbow surgery, but a right shoulder capsule sprain in mid-May delayed his eventual return. He's now hoping to throw an inning or two in a major-league game before the end of the season.