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Arizona Diamondbacks right-hander Zac Gallen was scratched from his scheduled spring training start on Monday because of soreness in his forearm caused by a hairline stress fractured at the radial head, the team announced on Tuesday. Manager Torey Lovullo said Gallen will be able to continue to play catch at a low-intensity level while he recovers, though he did not offer a timetable for when Gallen might return to the mound.

Gallen, who has been undergoing treatment for the ailment for 10 days, first encountered his forearm soreness when he was swinging a bat, per MLB.com's Steve Gilbert. Pitchers will be hitting once again in the National League in 2021 after MLB refused to implement the universal DH despite using it as part of the health and safety protocols during the abbreviated 2020 campaign.

Gallen tended to feel it on the mound only when he throws his curveball, he noted.

The 25-year-old Gallen has developed into one of the game's top starters in a short time since debuting in 2019. In 27 career starts to date, he's accumulated a 2.78 ERA (162 ERA+) and has struck out nearly three batters for every walk issued. The Diamondbacks originally acquired Gallen at the 2019 deadline from the Miami Marlins, parting with shortstop prospect Jazz Chisholm to get the trade done.

With Gallen unable to pitch on Opening Day, the Diamondbacks will likely turn to veteran southpaw Madison Bumgarner in his place. Bumgarner received the nod last Opening Day after joining the Diamondbacks over the winter, though he then had a brutal debut season. In nine outings, he compiled a 6.48 ERA and zero quality starts.

Any kind of extended absence from Gallen would also damage the Diamondbacks' already-modest playoff odds. As it stands, SportsLine gives Arizona a 34 percent shot at making it to October. The Diamondbacks will ostensibly have to replace him with either Alex Young, Riley Smith, or Jon Duplantier.