Seattle Mariners reliever Gregory Santos throws during a game against the San Francisco Giants on April 4 at Oracle Park. Bob Kupbens-Imagn Images

Flame-Throwing Seattle Mariners Reliever Near Return After Lengthy Layoff

Originally posted on Seattle Mariners on SI
By Teren Kowatsch | Last updated Aug 22, 2025 9:45 PM ET

SEATTLE — There hasn't been a unit on the Seattle Mariners roster that's been more chaotic than the bullpen this season.

Due to the several injuries and inconsistencies from the starting rotation, the Mariners' bullpen has been relied on heavily. It was at or near the top of baseball in innings pitched for parts of the first half of the season. Several relievers, such as Matt Brash and Jackson Kowar, made their returns after lengthy injured list stints.

Another ailing hurler could make is way back to the bullpen from his own ailment in the coming weeks.

Right-handed reliever Gregory Santos has been out since April 16 due to a right knee injury. He underwent surgery to clear up cartilage in his knee, and has been recovering since.

Santos had to return to the Dominican Republic due to a personal matter, and his rehab and ramp-up was delayed as a result.

Santos returned to Arizona and looks to be back on track for a return sooner rather than later.

"Very competitive bullpens (in Arizona)," Seattle general manager Justin Hollander said in a pregame news scrum Friday. "Had a really good week last week. Would anticipate a rehab assignment, with that leading into (hopefully) a September return."

Looks like Gregory Santos is throwing in AZ. Wonder if we could see him in Tacoma soon pic.twitter.com/ofdHjhvHKQ
— Ben Ranieri (@BenRanieri10) August 19, 2025

Hollander said the potential September return would be closer to the middle of the month depends on how Santos feels and responds to ramping up.

Santos was acquired by the Mariners in a trade with the Chicago White Sox on Feb. 3, 2024. Santos was coming off his best pro season in 2023. He posted a 3.39 ERA with 66 strikeouts in 66.1 innings pitched across 60 appearances that year.

Santos is one of the strongest arms on the team and has touched triple-digits with his fastball, but he's been plagued with injuries since joining Seattle.

In his two years in the organization, Santos has had a right lat strain, right biceps inflammation and his current knee issue.

Santos has posted a 5.02 ERA and has fanned six batters in 14.1 innings pitched across 16 total outings for the Mariners in 2024 and '25.