The D-backs, though, are taking nothing for granted as they will continue to stretch out pitchers Randall Delgado, Archie Bradley and Bo Schultz just in case.
"We've got a lot of good options," D-backs manager Kirk Gibson said.
Those options could come into play under a couple of different circumstances.
For instance, Arroyo came down with a back issue Monday. At this point the injury does not appear to be serious or something that would put him in jeopardy of missing regular season starts, but it illustrates how easily injuries could happen, quickly changing the rotation equation.
The D-backs have announced that Corbin and Cahill will pitch the two regular-season games in Sydney, Australia, against the Dodgers on March 22 and 23, and the D-backs will likely carry an expanded bench and bullpen, rather than any of their other three starters, on the trip.
An issue could arise if Corbin or Cahill were to suffer a freak injury, or get sick, on the trip to Australia and be unable to pitch.
By keeping Delgado pitching as a starter until then, he would be stretched out enough to fill in if need be, but, if not, he could pitch out of the bullpen.
"It gives us more flexibility looking into our Sydney roster," Gibson said. "One of the things we want to prevent is we get over there and we don't have guys built up enough so if we have someone gets hurt..."
The team has been intrigued with the idea of Delgado as a reliever for a while now.
"He very well could be in the bullpen for us this year," Gibson said. "We've always had [Josh Collmenter] as our only long guy. You'd rather have another guy to have some length in his arm."
Delgado figures to be on the Opening Day roster one way or the other, given that he is out of Minor League options and would need to clear waivers if the team tried to send him to the Minors.
"I'm just trying to do the best I can do as a starter right now and then if I end up a reliever it's OK," Delgado said. "I won't complain about it."
Delgado has been intriguing as a reliever because at this point he is still trying to get a consistent third pitch, something that is usually necessary for a pitcher to be successful as a starter, but not as a reliever.
With a good fastball and outstanding changeup, Delgado would not need to rely on the inconsistent changeup out of the bullpen. In addition he would likely gain some velocity with his fastball, if he only has to throw it in short one- or two-inning relief stints.
"I think Randall has kind of a Collmenter mentality, where regardless of where you put him, I think he'll adjust to that and do a very good job with it," Gibson said. "He just wants to pitch. He's young, he's aggressive, he's a developing pitcher. Because of where he is with options there's probably a good chance he'll be on the team."
Delgado started Tuesday's game against the Padres and allowed four runs on five hits. He gave up a pair of home runs, which was an issue for him last year when he allowed a whopping 24 in 116 1/3 innings.
While Bradley and Schultz figure to start the year in the Minors, they, too, have pitched well enough to be candidates, should an opening occur.
Bradley, ranked as the No. 1 pitching prospect in baseball by MLB.com, threw three scoreless innings Monday in his spring debut.
Meanwhile Schultz, who is 28 and has bounced around the Minors a bit, followed Bradley with a pair of scoreless innings of his own.