MLB Offseason Rumors: Mariners May Trade Star Pitcher

The Seattle Mariners have been through quite an exciting season. But they're slowly beginning to struggle down the stretch, and it could ruin all the work they've put in this year.

Either way, the Mariners are headed for an exciting offseason. They could lose players in free agency, but they could also add some. There are also some trades the Mariners could make in the coming months.

FanSided's Zachary Rymer recently predicted the Mariners would cut ties with veteran pitcher Luis Castillo in a blockbuster offseason trade.

Luis Castillo is the perfect trade candidate for the Mariners

Seattle Mariners pitcher Luis Castill — Aug 26, 2025; Seattle, Washington, USA; Seattle Mariners starting pitcher Luis Castillo (58) reacts after loading the bases with a walk against the San Diego Padres during the first inning at T-Mobile Park. Mandatory Credit: Joe Nicholson-Imagn Images | Joe Nicholson-Imagn Images

"The three players the Mariners got at the trade deadline — Eugenio Suárez, Josh Naylor, and Caleb Ferguson — are all slated for free agency, and Jorge Polanco and Mitch Garver are likely to leave via the open market as well," Rymer wrote. "Yet Castillo is the pick here because A) he represents less of a layup and B) there’s precedent for the Mariners to trade pitchers they don’t want to pay anymore.

"They did it with Robbie Ray in January of 2024, at which time he was two years into a five-year, $115 million deal and recovering from Tommy John surgery. Though Castillo, 32, is a different case in that he’s perfectly healthy, his fastball is waning and his effectiveness is going with it. The M’s didn’t have an easy time trading him last winter, but the difference this time is that he’ll “only” have $48.3 million owed to him through 2027. Castillo does have full no-trade protection for the rest of this year, but not after the calendar turns to 2026."

Castillo has been solid this year, but his underlying metrics indicate that he's heading for a downward spiral. The righty has helped the Mariners win games, but Seattle has a loaded farm system of pitchers, including Kade Anderson.

With Anderson and other top prospects banging on the door of the big leagues, Castillo will be a tradable asset. There should be some teams around the league with interest in the veteran righty, but the Mariners might have to accept a low-ball offer to move him and his contract off the payroll.

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