Wednesday, Dr. David Altchek confirmed the first opinion that Walker would need Tommy John surgery and be out at least for the next 12 months.
"It was very disappointing especially how I felt," Walker said. "It didn't feel that serious. It still doesn't, but the MRI showed a pretty big tear in there, and I think the best option is to get it done, get it fixed and rehab and be ready to come back next year."
D-backs manager Torey Lovullo also said he was surprised by the severity of the injury.
"It's a tough situation for all of us to walk through," Lovullo said. "I asked him to stick around. I asked him to be around because I want to make sure that we help him out through these tough days."
Dr. Altchek will perform the surgery next Wednesday in New York.
"It's going to be a long process," Walker said. "It's going to be a long journey, but I've got a really good support system here with the guys."
Matt Koch will start in Walker's place Friday against the Padres. It's possible the D-backs could shuffle starters in that fifth spot until deciding on a permanent solution. That's what they did last year, using Braden Shipley and Zack Godley before finally deciding on having Godley fill the role.