D-backs' Young Righty Had Serious Difficulties in 2025

The Arizona Diamondbacks' righty had a very small major league role, but had a difficult 2025 as a whole.

Jul 22, 2024; Kansas City, Missouri, USA; Arizona Diamondbacks starting pitcher Yilber Diaz (45) pitches during the first inning against the Kansas City Royals at Kauffman Stadium. Mandatory Credit: Jay Biggerstaff-Imagn Images | Jay Biggerstaff-Imagn Images

The Arizona Diamondbacks needed a massive number of players to manage to get through a brutal 2025 season.

A year filled with injuries, underperformance and overall disappointment despite pre-season hopes ended with an 80-82 record, as Arizona sat at home watching the playoffs from afar for the second straight season.

With so much roster turnover, there were many players (particularly pitchers) who came in and out of the roster. One such little-utilized arm was embattled right-hander Yilber Diaz, whose 2025 season was full of ups and downs at the minor league level.

Diaz appeared in just one game for Arizona's bug league club.

As Arizona Diamondbacks On SI breaks down each individual season from the entirety of the 2025 roster, the below article will be updated with the proper links as the season reviews are published:

Related Content: Breaking Down Every Diamondbacks Player's 2025 Season

Arizona Diamondbacks 2025 Player Review: Yilber Diaz

Arizona Diamondbacks right-hand pitcher Yilber Diaz | Alex D'Agostino

Diaz's first taste of the major leagues in the 2024 season was relatively successful. Though not elite, he posted a 3.81 ERA over seven appearances (four starts) including two quality starts.

So there was some level of expectation he'd be able to compete for a role in 2025. Diaz was called up briefly near the beginning of the season, coming in for three innings of relief on April 25. He gave up three runs in that time on four hits and three walks.

He was sent back to the minor leagues, and from there, his season imploded. Diaz was knocked around in Reno, sent back to the Arizona Complex League to work on his command, and returned with similar issues.

It got so difficult, he was demoted to Double-A, where he posted a 6.43 ERA in a short relief role. An arm that appeared to be on the cusp of emerging as a true major-leaguer looked out of sorts for the majority of the 2025 season.

Yilber Diaz: 2026 Outlook

Diaz ultimately posted an 11.63 ERA for the Aces, walking an unbelievable 64 batters over only 41 innings. He walked nine in 14 Double-A innings.

Diaz has quality stuff, but that serious of a command issue seems to have set back his path to the majors. With some rapid development, it's not out of the question to see him back on the MLB roster, but it's going to take some major strides in the command department.

Perhaps a "fresh" start in the 2026 season could be what he needs. Clearly, there was a confidence issue in addition to his mechanics.