MESA, Ariz. -- Zac Gallen, the D-backs' best pitcher last season, was scratched from his scheduled start on Monday with soreness in his right lateral forearm, a concerning development with Opening Day quickly approaching.

Gallen had an MRI taken on Sunday and a CT, along with X-rays, on Monday, and the team is still awaiting an official diagnosis. Losing Gallen for any period of time would be a blow to the D-backs.

In 12 starts last year, Gallen was 3-2 with a 2.75 ERA, and he finished ninth in the National League Cy Young Award voting.

"It's just not the news you want to hear," manager Torey Lovullo said. "You want to start having guys prep and get ready for the season. So I'm not going to sugarcoat it and say that it's OK. We're obviously going to get him evaluated and figure out what the best thoughts are moving forward. And we don't know any of this information right now. So yeah, it's not it's not anything I was prepared to hear today."

Gallen said he first started feeling discomfort when he was jammed by a pitch while taking batting practice off a pitching machine on March 10.

The right-hander didn't think much of it and went ahead and made his scheduled start on March 12. The only time Gallen felt discomfort when pitching was when he threw his curveball. He started getting treatment the following day, and he made his scheduled start St. Patrick's Day against the Rangers.

"I just thought it was something like always, you know, just get jammed, go away in a couple days," Gallen said. "I was fine pitching on it. Like I said the other pitches felt perfectly OK, but it was just kind of lingering and so we figured let's take a deeper dive and see what we got here."

Anytime a pitcher has forearm soreness, it obviously raises concern. But until all the information is known, Gallen does not want to get too far ahead of himself, especially since only the curveball has been the issue.

"I don’t think we have all the information so it’s tough to say, but I think it’s definitely a positive that I’ve pitched with it, pitched in two games now," Gallen said. "The rest of my stuff has felt fine. The rust is coming off and those pitches were feeling better, so I think that in and of itself was a positive. Of course, you’re going to be concerned, probably overly concerned than maybe one needs to be. At the same time, I know between the training staff here and the training staff at my agency, everyone is going to put me in the best hands possible to get this figured out and get me back to 100 percent, and back on the field as healthy as one would hope to be."

The D-backs' rotation had been seemingly set coming into camp with Madison Bumgarner, Gallen, Merrill Kelly, Caleb Smith and Luke Weaver lined up.

Knowing it would need starting pitching depth, though, Arizona has stretched out 14 pitchers as starters even though some of them will likely end up in the bullpen.

Taylor Clarke and Taylor Widener would seem to be the most logical candidates to fill in if Gallen has to miss time. Both have been starters before in the Minor Leagues and have pitched well this spring.

"We’re in good shape," Lovullo said. "If we have to pivot, we’re in a good spot. We’re going to have a lot of guys who are stretched out and ready."