Arrieta has been limited this year by a bone spur in his right elbow that has been both painful and damaging to his pitching.
"Yeah, it hurts every day," the pitcher said after his most recent start against the San Francisco Giants, per Jim Salisbury of NBC Sports. "Today, I lacked the ability to throw any off-speed stuff with effectiveness, and they made me pay for it."
He allowed five runs in just three innings during Sunday's start, the eighth time opponents scored at least five runs against him in his 24 starts.
This was not what the Phillies anticipated when they signed the right-hander to a three-year, $75 million deal.
Arrieta had an up-and-down first season with the team, finishing 2018 with a 3.96 ERA and a 10-11 record. This was worse than any of his four-and-a-half years with the Chicago Cubs, which featured a combined 68-31 record and a 2.73 ERA.
He also won the Cy Young Award in 2015 and was a key part of the World Series title run in 2016.
While he still possesses upside, the 33-year-old has major question marks about his health. Meanwhile, the team's rotation is even thinner behind Aaron Nola. Midseason additions Drew Smyly and Jason Vargas become even more important heading into the final stretch of the season.