Arizona Diamondbacks right-hander Taijuan Walker has a partial tear of the ulnar collateral ligament in his pitching elbow and will need Tommy John surgery, manager Torey Lovullo announced Wednesday.
Walker underwent an MRI on Tuesday, then traveled to New York to get a second opinion that confirmed the injury. He has been on the 10-day disabled list since Sunday with what the team initially described as forearm tightness.
"It's terribly disappointing," Lovullo said. "I hurt for him. I think this organization hurts for him. ... It's one of your players going down that we were going to count on. He's hurting. When he hurts, we all are. We're going to support him in the best situation we can, but this is a tough situation we're walking through."
Walker, 25, has a 3.46 ERA in three starts this season, his second with the Diamondbacks.
The team announced that Matt Koch will take Walker's spot in the rotation Friday when the Diamondbacks host the San Diego Padres.