Update: Walker is expected to undergo Tommy John surgery after all. He will miss the rest of the season and at least the first month of the 2019 campaign:
Torey Lovullo announces Taijuan Walker has a torn UCL and will likely undergo Tommy John surgery.
— Arizona Diamondbacks (@Dbacks) April 18, 2018
Here's some troubling news regarding Diamondbacks right-hander Taijuan Walker ...
Dbacks manager Torey Lovullo says Taijuan Walker has a “UCL injury”. Doesn’t know if it’s a tear. Says he was just told it was a UCL injury.
— Steve Gilbert (@SteveGilbertMLB) April 17, 2018
As Gilbert later tweets, Walker went to New York on Tuesday for a second opinion, which should provide more clarity. Obviously, significant tears to the UCL typically lead to Tommy John surgery, but the extent of Walker's injury isn't yet known.
Suffice it to say, losing Walker would be a big blow to the first-place Diamondbacks. The 25-year-old Walker this season has pitched to a 3.46 ERA/124 ERA+ after three starts. For his career, he owns an ERA+ of 105 across parts of six seasons. The Diamondbacks acquired Walker prior to the 2017 season as part of a trade with the Mariners.
Even if Walker avoids the worst-case scenario, he's likely in for a significant stay on the disabled list. The rotation as presently assembled is a pronounced strength for Arizona, but depth is a concern, at least until Shelby Miller returns from his May 2017 Tommy John surgery. If they lose Walker for a while, then the D-Backs would likely turn to Braden Shipley, Troy Scribner, Kris Medlen, Taylor Clarke, or Matt Koch to fill his spot.
