The shortstop was acquired from the Reds as part of a three-team trade in which the Diamondbacks surrendered Trevor Bauer and a couple other arms. According to GM Kevin Towers, the team did not perform a physical on the young shortstop prior to acquiring him from Cincinnati, so there's no knowing whether the strain was present before he was dealt.
The article mentions that Gregorius was a long-shot to make the Opening Day roster anyway, but this injury makes that even less likely. The Diamondbacks also acquired Cliff Pennington from Oakland this offseason, and he could take over at shortstop in the short-term.
Arizona has been active this offseason, trading away Justin Upton, Bauer, and Chris Young. The team has been reshaping itself in GM Towers' image, which could be either exciting or terrifying to watch for Arizona fans this summer.
Gregorius, 23, appeared in eight games last season for the Reds, but the Diamondbacks were planning on giving him more at-bats at Triple-A to get things sorted out before he received a call to the Major Leagues.