"We haven't talked about it," manager Kirk Gibson said when asked who would start Sunday. "It's possible he could start again, but it hasn't been determined. A lot depends on how we get through the weekend."
Delgado had battled for the No. 5 spot in Spring Training, but he struggled with his command and lost out to Patrick Corbin.
When the D-backs needed a bullpen arm earlier this month, Delgado was called up from Triple-A Reno, and he made one appearance before being sent back down.
Delgado showed excellent control Tuesday by not issuing a walk and while he has made some mechanical adjustments since the spring, that was not the main reason for his improvement.
"I tried everything, but I think it was more mental," Delgado said. "When you get confidence, you feel better. It's not so much about mechanics, it's more about being confident."
Steve Gilbert is a reporter for MLB.com. Read his blog, Inside the D-backs, and follow him on Twitter @SteveGilbertMLB. This story was not subject to the approval of Major League Baseball or its clubs.