The loss of Arroyo is yet another blow to an Arizona team that has the second-worst record in baseball at 37-53 and has already begun trading away veteran players. The Diamondbacks sent reliever Joe Thatcher and outfielder Tony Campana to the Los Angeles Angels and dealt starter Brandon McCarthy to the New York Yankees over the weekend.
Arroyo said Monday that an MRI revealed the ulnar collateral ligament had torn completely off the bone and that he will have surgery in the next week or so.
He also said he believes he tore the ligament during a start against Washington in May, when he outpitched Stephen Strasburg in a complete-game victory. He made six more starts before going on the disabled list. He was still effective, despite a steady drop-off in velocity, using deception to fight off hitters and medication to fight the pain. He went 3-0 with a 2.95 ERA over his final three starts.
"We had a discussion with him before his last start, and he was pretty adamant about continuing to pitch; he thought he could get through it, but that last game really hurt him," Diamondbacks manager Kirk Gibson said. "That's when we shut him down and got the MRI and we took this course. It seems that surgery is the only way to go now."
Even after the MRI revealed the tear, Arroyo tried to fight through it before succumbing to surgery.
"I wanted to see if I could pitch on it without the ligament, because a few guys have done it," Arroyo said. "Most of the guys were bullpen guys, so it was going to be tough to do. I fired it up the last three days, and I could throw 120 feet and I could probably go out there and pitch, but it just won't come back fast enough. So I'd have to pitch every 10 days and take nine days to get it healthy. It just wasn't going to work."
The right-hander was 7-4 with a 4.08 ERA in 14 starts this season, having gotten off to a slow start after suffering a back injury in spring training.
Arroyo, 37, signed a two-year, guaranteed $23.5 million contract with the Diamondbacks in February that includes an $11 million club option for 2016 with a $4.5 million buyout.
Entering this season, durability was Arroyo's trademark. He surpassed 200 innings in eight of nine seasons heading into 2014. The lone exception was 2011, when he battled valley fever, mononucleosis and a case of whooping cough that caused him to lose 17 pounds. He still made 32 starts and logged 199 innings that season.
Arroyo made 369 career starts during 15 seasons with four teams before going out June 16 with elbow tendinitis in his first career visit to the disabled list. That streak ranked second among active big league starters behind Mark Buehrle.
Patrick Corbin, Arizona's projected Opening Day starter, previously went down for elbow reconstruction surgery in March. Reliever David Hernandez also underwent the ligament-replacement procedure earlier this season.
Right-hander Daniel Hudson has had the surgery twice, in 2012 and 2013.
All three are working their way back to the big leagues, and Arroyo will do the same despite nearing the end of his career.
"If this was the last year that I was going to play, I would just go gut it out and pitch and it would hurt and I'd try to find a way to win at 82 miles per hour, but I don't think it is," Arroyo said. "I think my body's a lot younger than my age is. I think I'm probably closer to 32, 33 as far as the way I feel in comparison to most guys my age. So I don't think it's going to be a problem coming back."
Information from The Associated Press was used in this report.