Corbin said Sunday said he has a partial tear of the ulnar collateral ligament and is getting a second opinion with noted surgeon Dr. James Andrews before deciding whether to try to rehab the injury or have surgery.
"This all new to me," he said. "I've never been hurt before, so I'm just trying to get through it."
He called Sunday one of the "worst" days ever on Twitter.
Thank you everyone for the well wishes and prayers. One of the worst days ever, but I will overcome this. Just wish I could be with the team
- Patrick Corbin (@PatrickCorbin11) March 16, 2014
Corbin had been designated the team's Opening Day starter against the Los Angeles Dodgers in Australia, but left Saturday's game against Cleveland in the seventh inning with forearm stiffness.
He was 14-8 with a 3.41 ERA and made the All-Star team as a rookie last season.
"It's a big blow to the individual that he's going through this," manager Kirk Gibson said. "As a team, we've all prepared for him to be a part of it. ... We didn't see anything coming."
Gibson said left-hander Wade Miley will start Saturday's opener.
Corbin said he had experienced minor tightness in the arm but the condition grew more serious with his final three pitches on Saturday
"It felt like a small little shock in there. Nothing popped in there, just a different feel I wasn't used to, just really uncomfortable."
Corbin, who barely made the 2013 opening day roster, had a sensational start to last season, opening 9-0 and making the All-Star team. He struggled down the stretch, though, pitching a longer season than he ever had experienced.
Now, at age 24, Corbin faces the biggest challenge of his career.
"There's only two options," he said, "taking six weeks off, (then) rehabbing for six weeks, or having Tommy John."
General manager Kevin Towers said there were three "in-house" candidates to join the rotation -- top prospect Archie Bradley, right-hander Randall Delgado and Josh Collmenter, who normally is the long reliever. Corbin returned this season as the No. 1 starter, anointed early by Gibson to go in the opener. He had made an offseason trip to Australia to promote the game.
Gibson said there will be plenty of time on the long flights to and from Australia to discuss the situation.
Corbin said he has talked to teammates Daniel Hudson and Matt Reynolds about how to deal with the injury. Both are recovering from the same surgery that Corbin may have. Hudson needed a second operation.
Reynolds said he knows how Corbin is feeling.
"It's probably one of the low points in your career," Reynolds said. "It's a major, serious injury and you're at the very beginning thinking it's going to be a long time. It's a tough day. There's a million things going through your mind."
Miley, who wasn't even scheduled to make the Australia trip, was the obvious choice to replace Corbin, Gibson said. Miley was 10-10 with a 3.55 ERA last season after going 16-10 as a rookie in 2012.
"Obviously you never want to see anything like that happen to any of your teammates," Miley said. "It's unfortunate. He's a big part of this team. .. But I guess it's something you've got to deal with, and you move on."
Information from The Associated Press was used in this report.