Servais said Paxton will have surgery on his left elbow, but did not say Tommy John.
Paxton, 32, went on the 10-day injured list Wednesday with a forearm strain in his pitching arm after leaving his first start of the season in the second inning after 24 pitches.
Paxton was 41-26 with a 3.42 ERA for the Mariners from 2013 to 2018, striking out 617 and walking 168 in 582⅓ innings. He was traded to the New York Yankees in November 2018 for a top prospect, left-hander Justus Sheffield, along with outfielder Dom Thompson-Williams and right-hander Erik Swanson.
Paxton struggled in the first half of his first season in New York, rediscovered his breaking ball in the second half and went 15-6 with a 3.82 ERA. He won a career-best 10 straight starts before leaving his final regular-season start after one inning on Sept. 27, 2019.
The Yankees said he had a tight left glute muscle, and he returned to go 1-0 with a 3.46 ERA in three postseason starts, allowing five runs in 13 innings. But he needed surgery in February 2020, when Dr. Andrew Dossett in Dallas performed a microscopic lumbar discectomy to repair a herniated disk and remove a peridiscal cyst.
Paxton was able to start the season on time when the COVID-19 pandemic caused a delay until late July, but he went just 2-3 with a 6.64 ERA in five starts. He did not pitch after Aug. 20 after suffering what the Yankees said was a low-grade strain in his left forearm flexor.
He returned to the Mariners this offseason on a one-year deal.
Information from The Associated Press was used in this report.