SCOTTSDALE, Ariz. -- The D-backs have yet to name an Opening Day starter, but they know it won't be ace Zack Greinke, still recuperating from a groin injury that knocked him from a start earlier this spring.
Greinke, who threw in a "B" game on Wednesday, was notably critical of his own performance and status in his rehab. D-backs manager Torey Lovullo quickly refuted those concerns.
"Zack is a great pitcher. Zack is an elite pitcher," Lovullo said. "The track record will show he's one of the best for a long period of time. When you probably experience things that aren't flowing the way that you want, you self-evaluate and become very critical. I don't know anybody in this room who is as great as he is at his craft. So I can't experience that. I don't know what that feels like. But he is an elite pitcher who is probably experiencing a little bit of frustration to get back to that level. He will get back to that level."
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While Lovullo was bullish on Greinke's ability to overcome his minor injury and return to his Cy Young-level form, he remained cautious when talking about his next start. His next turn to take the mound would appear to be Monday at Chase Field, as Arizona hosts Cleveland in an exhibition game, though Lovullo wouldn't commit to that date.
"We just don't want to put him in a position where if he starts to feel a little bit of discomfort, we're going to force that day," Lovullo said of the right-hander, who is still expected to make his first regular-season start during the club's first turn through the rotation. "I don't want to get married to that day with you guys. But we definitely want to get him on the mound again one more time. When that happens, we're not exactly sure.
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"He had a little injury and who knows when it's going to pop up. I want to protect us and protect Zack the best way that I can. I probably wouldn't have made the comment I made now about how great he is and the frustration he's experiencing had he made those comments. But I think Zack is a pretty special pitcher and a pretty special guy. He's going to wind up on the right side of this as soon as possible."
Walker on the attack
In what was his final appearance on the Salt River Fields mound this spring, D-backs right-hander Taijuan Walker couldn't help but be encouraged.
He allowed three runs, including a homer to Yoan Moncada in the fifth, and worked around hard contact over 5 2/3 innings in a 3-1 loss to the White Sox on Thursday. He built his pitch count up to 90, and his next start will likely come on the mound at Chase Field on Tuesday, as the club hosts the Indians in its final exhibition before Opening Day on Thursday.
"I was aggressive with the fastball, attacked," Walker said. "I felt really good with it, thought the fastball was coming out really good and I was locating it well. I tried mixing in some offspeed pitches. The curveball, I was spiking it a little bit, so I just tried throwing some in there for strikes. My stuff got better towards the end of the game. I feel good with all my pitches right now."
He yielded nine "hard-hit" balls, otherwise known as balls in play with an exit velocity of 95 mph or greater according to Statcast™, but did induce seven swings and misses over the course of the evening and finished with seven strikeouts.
"Taijuan's stuff looked really sharp and aggressive," Lovullo said. "He came out and attacked with his fastball, and his secondary stuff started to develop throughout the outing. He had a nice blend of pitches. That's what you want to see."

Koch optioned
Arizona optioned right-hander Matt Koch to Triple-A Reno on Thursday.
The D-backs' roster sits at 34 with the move, needing to come down to 25 before the season begins. Koch, who has worked as a starter, had no clear way to cut into an established rotation of Greinke, Robbie Ray, Zack Godley, Walker and Patrick Corbin, even with Greinke's recent injury.
The 27-year-old struggled in his final Cactus League outing on Wednesday against the Giants, allowing five runs on six hits, including a pair of homers to Joe Panik and Andrew McCutchen, in three innings. He went 2-1 with a 4.40 ERA over six Spring Training appearances (four starts).
Worth noting
• D-backs catcher Jeff Mathis, who had been dealing with some nagging back tightness, had five at-bats in a game on the Minor League back fields at the club's Salt River Fields facility on Thursday.
"I saw a couple of at-bats and I was very encouraged that he was able to control the barrel and get through the ball and use his legs," Lovullo said.
• Reliever Randall Delgado, likely to start the season on the disabled list with an oblique injury, is expected to throw a bullpen session on Sunday, Lovullo said. Delgado posted a 3.59 ERA in 26 appearances (five starts) last season before being shut down with elbow inflammation.
• Outfielder Jarrod Dyson left the team facility after Thursday morning's workout to attend to a family matter, Lovullo said. The outfielder, who signed a two-year, $7.5 million deal this offseason, is expected to rejoin the club on Sunday evening as the team returns to Chase Field for its final exhibition games.
Up next
Corbin will make his final spring start on Friday when the D-backs take on the Indians at 6:05 p.m. MST. The lefty has allowed four earned runs over six innings while striking out five in his two Cactus League starts.