The Arizona Diamondbacks will face several roster decisions this offseason, although some appear much easier to predict than others.

Arizona has many members of its active roster under contract for the 2027 season. Their manager Torey Lovullo is back, but Arizona also has several players with expiring agreements who could be retained through new deals.

However, Zac Gallen appears almost certain to depart.

Gallen re-signed with Arizona before the 2026 season after producing what was, at the time, the worst year of his career in 2025. He finished that season with a 4.83 ERA and 1.26 WHIP in 192 innings over 33 starts.

The Diamondbacks gave him a one-year contract worth approximately the same as the $22.025 million qualifying offer, with part of the money deferred. The decision ultimately failed to produce the result Arizona wanted.

Gallen regressed even more, going 3-9 with a 6.07 ERA and 1.55 WHIP in 105.1 innings over 22 appearances (20 starts) during the 2026 season.

He recorded 64 strikeouts and 35 walks while continuing to experience many of the same problems that affected him the previous year.

His fastball remained ineffective, while his breaking pitches no longer deceived hitters consistently. A right elbow injury also forced Gallen to miss significant time.

Shortly after returning from the injury, the Diamondbacks removed him from the starting rotation and moved him to the bullpen. He pitched only four innings over two relief appearances.

Gallen is not under contract for the 2027 season and appears extremely unlikely to return to Arizona following two consecutive disappointing years.

What happened over the last two years doesn’t erase the fact that Gallen was an important part of the Diamondbacks’ rotation. Gallen built his reputation through preparation, competitiveness and the ability to challenge hitters with a clear plan.

He also handled the responsibility of taking the mound as one of Arizona’s leading starters. That role demands accountability because difficult performances cannot be hidden when a pitcher is expected to provide stability every fifth day.

Gallen’s willingness to return on a one-year agreement showed confidence in his ability to recover from a poor season. The outcome did not match that belief, but accepting the challenge still required considerable self-assurance.

His move to the bullpen also demanded adaptability. A veteran starter can struggle with an unfamiliar routine, shorter preparation window and uncertainty over when he will enter a game.

The diminished effectiveness of Gallen’s pitches and his right elbow injury ultimately outweighed his previous accomplishments. Arizona needs dependable rotation production, and another reunion would require trusting that he can reverse two years of decline.

Both sides would benefit from a change. Gallen can seek a fresh environment, while the Diamondbacks can redirect their resources toward a more reliable starting option.