PHOENIX -- An MRI taken of D-backs right-hander Zack Greinke’s abdominal muscle came back “clean," manager Torey Lovullo said, and the team is optimistic that Greinke will be able to take his next turn in the rotation.

The news, however, was not as positive when it came to the MRI of Taijuan Walker’s shoulder.

Walker, who is recovering from Tommy John surgery last May, left a rehab start Wednesday with shoulder soreness.

An MRI revealed he has a capsule sprain in the shoulder, and he received a platelet-rich plasma injection. Walker will not be able to throw for six weeks and then will have to essentially restart his throwing program.

“Really unfortunate for him,” Lovullo said of Walker. “He's been working his tail off to get back here. This is just a bump in the road for him, I know, and I know he's going to work hard to make good things happen as soon as he can.”

The D-backs were not counting on Walker’s return for the next four or five weeks, but after that, his absence will be felt in their starting pitching depth.

As for Greinke, he was scheduled to play catch Friday and then throw a bullpen session Saturday. If that goes well, he could make his next scheduled start.

“If he throws his bullpen tomorrow and comes out fine, I wouldn’t see why we would be looking at -- we have the ability to shift around the rotation just because of the off-day, but I wouldn’t imagine it would be an extensive change,” D-backs GM Mike Hazen said. “If the bullpen tomorrow doesn’t go exactly how we need it to, then we’ll be adjusting.”

Of more immediate concern is who will start Saturday night’s game against the Giants.

It appears the D-backs are leaning towards Zack Godley getting the ball, but that could change if he’s needed in relief Friday night.

“We're in an all-hands-on-deck situation right now,” Lovullo said.