Arrieta is expected to be ready for spring training.
The right-hander was placed on the injured list Wednesday, and before he underwent an MRI on Thursday, he thought his season was over.
"I'll probably miss the remainder of the season," Arrieta said Wednesday, per Mark Gonzales of the Chicago Tribune.
Arrieta has had his worst year since he emerged with the Chicago Cubs in 2013. In 24 starts, he is 8-8 with a 4.64 ERA and 1.47 WHIP, both his worst marks in five-plus years.
He last pitched Sunday, allowing five earned runs in three innings against the San Francisco Giants. That outing signaled to the veteran that it was time to address the injury, and he said, per NBC Sports Philadelphia's Jim Salisbury:
"I wanted to try and make it work for as long as possible while I could remain effective and help the team. After my start in San Francisco, I realized that I'm not able to give the team what it needs. I'm confident and we're confident that we have options that can contribute to a further level than I was able to. The pain is something I can deal with, but it's the loss of feel and the ineffectiveness as the outings wear on."
As Arrieta's ERA and WHIP have gone up each season since 2015, there have been questions as to whether age or usage caused a decline in performance. Arrieta, though, said the surgery should help him return to his old form:
Arrieta can opt out of his deal after this season. If he stays with the Phillies, he will be owed $20 million for 2020, and the club has contract options for 2021 and 2022 at $20 million apiece.
Even though Arrieta was not pitching like he did in winning the 2015 National League Cy Young Award, his absence will be a blow to the rotation. Philadelphia starters rank 16th in the majors with a 4.56 ERA.
The Phillies (64-58) are tied with the Cubs for the second NL wild-card spot.