When Corbin Burnes, Zac Gallen Will Make First AAA Rehab Starts

The Arizona Diamondbacks' starting rotation is in a state of flux, but two of their injured arms are progressing back towards an eventual major league return.

Right-handed ace Corbin Burnes has not appeared for the Diamondbacks since June 1 of 2025, when he went down with an elbow injury that required Tommy John surgery.

Fellow righty and former Arizona ace Zac Gallen has been on the IL since July 12 of this season with elbow inflammation that did not require surgery.

Here's when both of those two arms will make their first rehab starts — an important step toward an eventual return to major league action.

When Corbin Burnes will make first rehab start

Arizona Diamondbacks' Corbin Burnes (39) pitches against the Washington Nationals at Chase Field in Phoenix on June 1, 2025. | USA TODAY Network via Reuters Connect

According to a new report from Steve Gilbert of MLB.com, Burnes is scheduled to appear for Triple-A Reno on Saturday. It will be his first appearance in a minor league game since 2019; he has not spent much time on the IL in his illustrious career.

Burnes had initially intended to return around the time of the All-Star Break, but a shoulder injury pushed that timeline back to September.

According to Gilbert, Burnes could speed his way back to the majors after that lone rehab appearance. He could start against the Houston Astros, a series spanning September 4-6. Burnes will not be ramped up to full starter's length by that time, and will likely only pitch around three innings.

Burnes pitched to a 2.66 ERA in his 11 starts with Arizona last season. It may take him some time to look like his most effective self again. His velocity was last seen in the low 90s, a few ticks down from his 94-96 MPH career norm.

Burnes is nearly finished with second year of his franchise-record six-year, $210 million contract. He has an opt-out following this season.

When Zac Gallen will make first AAA start

Jun 9, 2026; Miami, Florida, USA; Arizona Diamondbacks pitcher Zac Gallen (23) delivers a pitch against the Miami Marlins during the first inning at loanDepot Park. Mandatory Credit: Sam Navarro-Imagn Images | IMAGN IMAGES via Reuters Connect

According to Gilbert, Gallen is expected to pitch one day after Burnes in Triple-A on Sunday. He will likely make his return to the major league rotation against the Kansas City Royals on September 7-9.

Gallen's 2026 season was not going well. After a career-worst 2025 season, he posted a 6.34 ERA over his first 19 starts (98 innings) this season. That ERA was the worst qualified number in baseball at the time of his injury.

Gallen's ramp-up may be a bit more advanced than Burnes, considering its lesser severity. It is not known how long he would be expected to pitch as of this writing.

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