Delgado has made 17 relief appearances this year and his last start came on Aug. 22, 2015, when he filled in as a starter against the Reds.
"We felt like he was going to be the most prepared guy for that moment," D-backs manager Torey Lovullo said. "He's had some extended outings, he's been throwing the ball very, very well. We talk about giving us a chance to win a game and we feel like Randall will do that."
Even in a best-case scenario, the D-backs know that they are going to have to use several relievers to get through the game.
"What we're asking him to do is go as hard as he can for as long as he can," Lovullo said.
Delgado has taken over the multi-inning role in the bullpen from Archie Bradley, who has been shifted to more high-leverage and late-inning situations.
Delgado has a 4.05 ERA this year, but has a 0.63 mark over his last seven appearances.
Outfielder A.J. Pollock (right groin strain) has begun to do some light running. Taking batting practice will be the next step for him.
The D-backs are holding a Cow Milk Off on Tuesday afternoon at Chase Field. The event will not be open to the public.
Pitchers Andrew Chafin, J.J. Hoover and Bradley will compete and Shamrock Farms will donate a tanker truck filled with 6,000 gallons of milk to Feeding America member St. Mary's Food Bank in Phoenix.
None of the three claim to have much experience:
Chaffin: "Somebody said something about a cow-milking contest and I said, 'Pick me, it sounds fun. I want to do it.' It's pretty simple, you just grab the teat at the top and just kind of milk it down. I don't know, it seems pretty self-explanatory to me."
Hoover: "I've milked a couple of cows back when I was way younger and milked goats most recently at Brandon Phillips' son's birthday party. Maybe five animals I've milked in my life, but I've done it. I wouldn't say that I'm skilled."
Bradley: "I'm just going to grab and pull down. Hopefully milk comes out. That's the plan."
Lovullo was asked who he thought would win.
"Hoover," he said after taking a few moments to think about it. "Because he has a farm and has several cows. In fact I know he has several cows. So he's a cow owner, which doesn't necessarily mean that he's going to know how to milk the cow, but I feel like knowing J.J. I feel very strongly that he and his wife know how to do that."
Steve Gilbert has covered the D-backs for MLB.com since 2001. Follow him on Twitter @SteveGilbertMLB. This story was not subject to the approval of Major League Baseball or its clubs.