SATURDAY: Miller has, in fact, decided to undergo Tommy John surgery, writes FanRag’s Tommy Stokke. Details of the surgery are unclear, but he’ll miss the rest of 2017 and quite likely a portion of the 2018 season while he recovers.

THURSDAY: Diamondbacks right-hander Shelby Miller has been diagnosed with flexor strain and a partially torn ulnar collateral ligament, Miller himself tells reporters (Twitter links via FanRag’s Tommy Stokke). Miller is considering his options, including Tommy John surgery, and will make a decision sooner rather than later.

The 26-year-old Miller exited his most recent start due to forearm tightness and was quickly placed on the 10-day disabled list, though this new diagnosis guarantees that he’ll miss considerably more time than that — likely the remainder of the 2017 season unless he pursues a non-surgical route such as a platelet-rich plasma injection or stem cell treatment (neither of which would guarantee that he’d ultimately avoid surgery).

The news comes as a significant blow to the D-backs after Miller showed encouraging signs early in the season. After a dreadful first year in Arizona (6.15 ERA, 6.2 K/9, 3.8 BB/9), Miller was showing improved velocity and missing more bats early in the 2017 season. Through his first three outings, Miller logged a 3.50 ERA with a 17-to-7 K/BB ratio and a 48 percent ground-ball rate. His most recent outing, however, back on April 23, lasted just four innings as Miller issued five walks and saw his average velocity dip.

[Related: Arizona Diamondbacks Depth Chart]

With Miller out for a significant time regardless of his ultimate treatment option, the D-backs will have a vacancy in their rotation. Zack Greinke, Patrick Corbin, Robbie Ray and Taijuan Walker are presently occupying the top four slots, and right-hander Zack Godley was recalled to make a spot start yesterday (though he’s already been optioned out).

In addition to Godley, right-hander Braden Shipley (a former first-round pick that’s currently in Triple-A and made his MLB debut in 2016) and right-hander Archie Bradley could be candidates to join the rotation. Bradley has been lights out in a relief role early this season, though GM Mike Hazen very recently told the Arizona Repbulic’s Nick Piecoro that the organization still views Bradley as a starter in the long run.