Diamondbacks pause A.J. Puk’s rehab after left-shoulder discomfort, plan MRI

Arizona’s bullpen depth will have to wait a little longer, with the Diamondbacks pausing left-handed reliever A.J. Puk’s rehab after he reported left shoulder discomfort. The organization is sending him for an MRI, per Nick Piecoro of the Arizona Republic as cited in MLB Trade Rumors, a step that typically indicates the team wants clarity on the cause and severity of the new limitation before resuming baseball activities.

The complication matters not just because it delays Puk’s next milestone, but because his rehab already has its own timeline backdrop. Puk’s current recovery path references a prior elbow procedure, an internal brace operation that took place on June 20, 2025. With June now underway, he is approaching that one-year anniversary, making this shoulder issue a second, separate hurdle rather than a continuation of the original problem.

Puk’s role on the roster is central. As a relief pitcher, his value is tied to the ability to pitch on consecutive days during stretches of bullpen strain, handle high-leverage innings, and keep matchup plans intact. When a late-inning arm is sidelined, teams often have to reshuffle who handles the most critical outs, and those adjustments can ripple across the rest of the relief corps.

The Diamondbacks’ decision to pause rehab suggests the issue is significant enough that the team is not comfortable pushing through it in the short term. While the report characterizes the discomfort as left-shoulder related, no further diagnosis or timetable was provided in the available information beyond the planned MRI and the impact on a potential 2026 return.

From a baseball operations perspective, MRI results can shape everything that follows: whether the team treats the situation as a temporary inflammation issue managed with rest and rehab, or whether it reveals a structural problem that would require a longer, more cautious path. Even in the absence of definitive findings, the act of pausing rehab indicates the organization is prioritizing minimizing risk and preventing further irritation that could prolong the overall recovery.

The broader context is that offseason and early-season bullpen planning depends on assumptions about availability, especially for pitchers who are expected to anchor late-game roles. A delayed return can force the team to lean more heavily on other relievers, reshaping usage patterns and potentially affecting how the Diamondbacks manage leverage situations as the season progresses.

What to watch next is straightforward: when Puk receives the MRI, what it shows, and how the Diamondbacks respond in practical terms, such as whether he can resume throwing and bullpen sessions on an incremental schedule. If the results confirm a manageable issue, a gradual ramp-up could follow. If the MRI reveals something more involved, the club may need to revise expectations for when Puk can return to game action.

For now, the only confirmed elements are that Puk has left-shoulder discomfort, his rehab has been paused, and he will undergo an MRI. Until those results are known, any projection about his exact 2026 availability would be speculative. The Diamondbacks will likely treat this like the elbow recovery before it, focusing on measured progress rather than rushing an important bullpen contributor back into action.