Corbin Burnes’ Rehab Setback Likely Keeps Him Out Until September

The Arizona Diamondbacks’ rotation plans took another hit this week when right-hander Corbin Burnes suffered a setback in his recovery from Tommy John surgery, with the team saying he now will likely be out until September.

According to MLB.com’s Diamondbacks report by Steve Gilbert, Burnes was diagnosed with a strain of his right teres major muscle after feeling discomfort in his arm following a live batting practice session last Friday, or May 29. Before facing hitters, Burnes had completed 15 bullpen sessions as part of what had been a steady rehab progression. Subsequent testing revealed the strain. The teres major is a shoulder-area muscle that helps power the throwing motion.

The setback delays what had looked like a closer return for one of Arizona’s biggest investments. Burnes, the 2021 National League Cy Young Award winner, signed a six-year, $210 million contract with the Diamondbacks before the 2025 season and was expected to be a major piece of the rotation once he was healthy. Instead, his comeback timetable has been pushed back again.

Burnes is rehabbing from Tommy John surgery after making 11 starts for Arizona in 2025 before injuring his elbow. This latest issue is a new complication during that rehab, not a report of a renewed UCL injury. He had been working toward a midseason return in 2026 before the teres major strain changed that outlook.

Diamondbacks manager Torey Lovullo acknowledged the loss but said the club still has options in the rotation. MLB.com reported that Arizona currently has five starters in place, with Brandon Pfaadt having moved into bullpen depth.

“Those are big, big pieces for us,” Lovullo said. “So it’s a blow, and it’s something that we’re gonna have to deal with. It’s just what we do in this game, and we’ve got very qualified players in that clubhouse, and they’re gonna get some opportunities, and we’ve got five really good starting pitchers right now, and they’re doing a good job. I want that to continue.”

The timing is especially frustrating because Burnes had recently sounded eager to move beyond the early stages of rehab. Speaking on May 21, he said, “I’m sick of throwing bullpens... I shocked, I think, a couple people today with the velocity, but it’s been good. Now it’s kind of the point now where we’re making sure the shape of all the pitches are good.”

That made last week’s live batting practice session feel like another step toward his return. Instead, it became the point where Arizona’s hoped-for midseason boost was pushed back to at least September.